0% found this document useful (0 votes)

49 views89 pages

Lots of Questions

Uploaded by

Mira Maizar

We take content rights seriously. If you suspect this is your content, claim it here.

Available Formats

Download as DOC, PDF, TXT or read online on Scribd

0% found this document useful (0 votes)

49 views89 pages

Lots of Questions

Uploaded by

Mira Maizar

We take content rights seriously. If you suspect this is your content, claim it here.

Available Formats

Download as DOC, PDF, TXT or read online on Scribd

You are on page 1/ 89

Generated by Direct DocX to Doc

1. The Born-Haber cycle for the formation of sodium chloride from sodium and chlorine may be
represented by a series of stages labelled A to F as shown.
N a + (g ) + C l(g ) + e –
A
N a + (g ) + 12 C l 2 (g ) + e
F
B
N a(g ) + 12 C l 2 (g ) –
N a + (g ) + C l (g )
C
1
N a(s) + 2 C l 2 (g )
E
D
N aC l(s)
(a) (i) Write the letters A to F next to the corresponding definition in the table below

definition letter H/kJ mol–1

1st ionisation energy of
+494
sodium
1st electron affinity of
–364
chlorine
the enthalpy of atomisation
+109
of sodium
the enthalpy of atomisation
+121
of chlorine
the lattice enthalpy of
–770
sodium chloride
the enthalpy of formation of
sodium chloride
(3)

(ii) Calculate the enthalpy of formation of sodium chloride from the data given.

(2)

(b) The lattice enthalpies can be calculated from theory as well as determined
experimentally.

Experimental Theoretical
H/kJ mol–1 H/kJ mol–1
Sodium chloride –770 –766
Silver iodide –889 –778

Why is the experimental value of the lattice enthalpy of silver iodide (–889kJmol –1) so
different from the value calculated theoretically?

...................................................................................................................................

...................................................................................................................................
(2)

http://www.epingsoft.com
Generated by Direct DocX to Doc

...................................................................................................................................

...................................................................................................................................
(3)
(Total 10 marks)

2. (a) The Born-Haber cycle for the formation of sodium chloride is shown below.
N a + (g ) + C l(g ) + e –

1
N a + (g ) + 2 C l 2 (g ) + e –

–
N a + (g ) + C l (g )

1
N a (g ) + 2 C l 2 (g )

1
N a (s) + 2 C l 2 (g )

–
N a + C l (s)

Use the data below to calculate the lattice enthalpy of sodium chloride.

Value of the
enthalpy change
Enthalpy change
/kJ mol–1

Enthalpy of atomisation of sodium +109

1st ionisation energy of sodium +494

Enthalpy of formation of sodium chloride –411

Enthalpy of atomisation of chlorine +121

Electron affinity of chlorine –364

(2)

http://www.epingsoft.com
Generated by Direct DocX to Doc

(b) Sodium chloride and magnesium oxide have very similar crystal lattices. Suggest why
the lattice enthalpy of magnesium oxide is very much larger than that of sodium
chloride.

................................................................................................................................

................................................................................................................................
(2)

(c) The lattice enthalpy of silver iodide can be calculated but the experimental value does
not match the calculated value as well as those for sodium chloride match each other.

Explain why the calculated and experimental values for silver iodide are different.

................................................................................................................................

................................................................................................................................
(2)
(Total 6 marks)

3. (a) State Hess’s Law.

..................................................................................................................................

..................................................................................................................................
(2)

(b) Define the term standard enthalpy change of combustion.

..................................................................................................................................

..................................................................................................................................
(3)

(c) The equation for the combustion of ethanol in air is

C2H5OH(l) + 3O2(g)  2CO2(g) + 3H2O(l)

and the structural representation of this is:

H H

H C C O H + 3O O 2O C O + 3H O H

H H
http://www.epingsoft.com
Generated by Direct DocX to Doc

(i) Calculate the enthalpy change for this reaction using the average bond enthalpy
values given below.

Average bond Average bond

Bond Bond
enthalpy/kJ mol–1 enthalpy/kJ mol–1

CH +412 CC +348

CO +360 OH +463
OO +496 CO +743
(3)

(ii) Draw and label an enthalpy level diagram to represent this reaction.

en th a lp y

(2)
(Total 10 marks)

http://www.epingsoft.com
Generated by Direct DocX to Doc

4. In an experiment to find the enthalpy change when copper is displaced from a solution of
copper ions excess zinc was added to 50.0 cm3 of 1.00 mol dm–3 aqueous copper(ii)
sulphate in a plastic cup.

Zn(s) + Cu2+(aq)  Zn2+(aq) + Cu(s)

The temperature of the solution in the cup was measured every minute for 10 minutes with the
zinc being added after 3.5 minutes.

The temperature readings are shown on the graph below.

70
Tem p era tu re/°C

×
60 ×
×
×
×
×
50 ×

20 × × ×

10
0 1 2 3 4 5 6 7 8 9 10
Tim e/m in u tes

(a) Suggest two reasons why a series of temperature readings is taken rather than simply
initial and final readings.

First reason..............................................................................................................

................................................................................................................................

Second reason..........................................................................................................

................................................................................................................................
(2)

http://www.epingsoft.com
Generated by Direct DocX to Doc

(b) Use the graph to calculate the maximum temperature change, T, as the reaction takes
place.

T = ...........................................°C
(2)

(c) Calculate the enthalpy change for the reaction using the formula below, giving your
answer to an appropriate number of significant figures.

H = –4.18 × T kJ mol–1

(2)
(Total 6 marks)

5. (a) (i) Define the term standard enthalpy of formation, Hf .

..........................................................................................................................

..........................................................................................................................
(3)
(ii) The following table shows some values of standard enthalpy of formation.

Name Formula Hf /kJ mol–1

ethene C2H4(g) +52.3
hydrogen bromide HBr(g) –36.2
bromoethane C2H5Br(g) –60.4

Use the data in the table above to calculate the standard enthalpy change for the
following reaction.

C2H4(g) + HBr(g)  C2H5Br(g)

(2)

(iii) State the significance of the sign of the value obtained in part (a)(ii) above.

..........................................................................................................................
http://www.epingsoft.com
Generated by Direct DocX to Doc

..........................................................................................................................
(1)

http://www.epingsoft.com
Generated by Direct DocX to Doc

(b) Enthalpy changes can also be calculated using average bond enthalpy data.

Bond Average bond enthalpy/kJ mol–1

C == C +612
CC +348
CH +412
C  Br +276
H Br +366

Use the data in the table above to recalculate the enthalpy change for the reaction in part (a)
(ii).

C2H4(g)  HBr(g)  C2H5Br(g)

(3)

....................................................................................................................................

....................................................................................................................................
(2)
(Total 11 marks)

6. The formation of magnesium chloride from magnesium and chlorine may be represented by the
following Born-Haber cycle:

http://www.epingsoft.com
Generated by Direct DocX to Doc

M g 2 + (g ) + 2 C l(g ) + 2 e –

M g 2 + (g ) + C l 2 (g ) + 2 e – M g 2+ (g ) + 2 C l – (g )

M g (g ) + C l 2 (g )

M g (s) + C l 2 (g )

M g C l 2 (s)

(a) Define the terms:

Lattice enthalpy.

....................................................................................................................................

....................................................................................................................................
(3)

Enthalpy of atomisation.

....................................................................................................................................

....................................................................................................................................
(2)

(b) (i) Identify on the diagram the chance representing the enthalpy of atomisation of
magnesium.
(1)
(ii) Use the data below to calculate the first electron affinity of chlorine.

Value of the enthalpy

Enthalpy change change / kJ mol–1
Enthalpy of atomisation of magnesium +150
1st Ionisation energy of magnesium +736
2nd Ionisation energy of magnesium +1450
Enthalpy of formation of magnesium chloride –642
Enthalpy of atomisation of chlorine +121
Lattice enthalpy of magnesium chloride –2493

http://www.epingsoft.com
Generated by Direct DocX to Doc

(2)

Draw a Born-Haber cycle which could be used to determine the electron affinity of
hydrogen.

(3)
(Total 11 marks)

7. The reaction of an acid with a base to give a salt is an exothermic reaction. In an experiment to
determine the enthalpy of neutralisation of hydrochloric acid with sodium hydroxide,
50.0cm3 of 1.00 mol dm–3 HCl was mixed with 50.0 cm3 of 1.10 mol dm–3 NaOH. The
temperature rise obtained was 6.90 °C.

(a) Define the term enthalpy of neutralisation.

....................................................................................................................................

....................................................................................................................................
(1)

(b) Assuming that the density of the final solution is 1.00 g cm–3 and that its heat capacity
is 4.18 J K–1 g–1, calculate the heat evolved during the reaction.

(3)

(2)

(d) Suggest why sodium hydroxide is used in slight excess in the experiment.
http://www.epingsoft.com
Generated by Direct DocX to Doc

....................................................................................................................................

....................................................................................................................................
(1)
(Total 7 marks)

8. (a) (i) Define the term standard enthalpy of combustion.

............................................................................................................................

............................................................................................................................
(3)
(ii) The values for the standard enthalpy of combustion of graphite and carbon
monoxide are given belo

Hc /kJ mol–1

C (graphite) –394
CO(g) –283

Use these data to find the standard enthalpy change of formation of carbon monoxide
using a Hess’s law cycle.

1
C(graphite) + 2 O2(g)  CO(g)

(3)

(iii) Suggest why it is not possible to find the enthalpy of formation of carbon
monoxide directly.

............................................................................................................................

............................................................................................................................
(1)

(iv) Draw an enthalpy level diagram below for the formation of carbon monoxide
from graphite.

(1)

(b) Natural gas consists of methane, CH4. When methane burns completely in oxygen the
reaction occurs as shown in the equation

http://www.epingsoft.com
Generated by Direct DocX to Doc

CH4(g) + 2O2(g)  CO2(g) + 2H2O(l) Hc = –890 kJ mol–1

Methane does not burn unless lit.

Use this information to explain the difference between thermodynamic and kinetic stability.

....................................................................................................................................

....................................................................................................................................
(4)
(Total 12 marks)

9. A student was required to determine the enthalpy change for the reaction between iron and
copper sulphate solution.

The student produced the following account of their experiment.

A piece of ir on, mass about 3 g, was placed in a glass beaker . 50 cm3 of
0.5 mol dm–3 aqueous copper sulphat e solut ion was measur ed using a
measur ing cylinder and added t o t he beaker . T he t emper at ur e of t he
mix t ur e was measur ed immediat ely bef or e t he addit ion and ever y minut e
af t er war ds unt il no f ur t her change t ook place.

F e + CuS O 4 F eS O 4 + Cu

T iming bef or e 1 min 2 mins 3 mins 4 mins 5 mins

addit ion
T emper at ur e/ °C 22 27 29 26 24 22

(a) Suggest two improvements you would make to this experiment. Give a reason for each
of the improvements suggested.

Improvement 1 ...........................................................................................................

....................................................................................................................................

Reason 1 ....................................................................................................................

....................................................................................................................................

Improvement 2 ...........................................................................................................

....................................................................................................................................
http://www.epingsoft.com
Generated by Direct DocX to Doc

Reason 2 ....................................................................................................................

....................................................................................................................................
(4)

(b) In an improved version of the same experiment a maximum temperature rise of

15.2 °C occurred when reacting excess iron with 50.0 cm3 of 0.500 mol dm–3
aqueous copper sulphate solution.

(i) Using this data and taking the specific heat capacity of all aqueous solutions as
4.18 Jg–1 deg–1 calculate the heat change.

(1)

(ii) Calculate the number of moles of copper sulphate used.

(1)

(iii) Calculate the enthalpy change of this reaction in kJ mol–1.

(2)
(Total 8 marks)

10. (a) Define the term standard enthalpy of combustion, making clear the meaning of standard in
this context.

………….…………………………………………………………………………..

………….…………………………………………………………………………..
(3)

(b) Use the enthalpies of combustion given below to find the enthalpy change for
the reaction:
2C(graphite) + 2H2(g) + O2(g)  CH3COOH(l)

Hcombustion/kJ mol–1
C(graphite) –394
http://www.epingsoft.com
Generated by Direct DocX to Doc

H2(g) –286
CH3COOH(l) –874

(3)

………….…………………………………………………………………………..
(1)

(d) Draw an enthalpy level diagram to represent the enthalpy change for the combustion of
graphite. Show both the enthalpy levels of the reactants and products and an energy
profile which represents the activation energy for the reaction.

(3)
(Total 10 marks)

11. (a) This question is about finding the formula of copper hydroxide. The method is as follows:

http://www.epingsoft.com
Generated by Direct DocX to Doc

20.0 cm3 of an aqueous solution of a copper salt of concentration 1.00 mol dm–3 was placed
in a polystyrene cup and its temperature measured using a thermometer graduated in
0.1 °C intervals.

A burette was filled with aqueous sodium hydroxide, of concentration 2.00 mol dm–3.

2.00 cm3 of sodium hydroxide solution was run into the solution of the copper salt and the
temperature was measured immediately.

As soon as possible a further 2.00 cm3 of sodium hydroxide solution was run in and
the temperature measured again.

This process of adding 2.00 cm3 portions of sodium hydroxide solution and measuring the
temperature was continued until a total of 36.0 cm3 of the sodium hydroxide solution
had been added.

The temperature readings are shown in the graph below.

http://www.epingsoft.com
Generated by Direct DocX to Doc

29
Te m p e ratu re / ºC
28

20
0 4 8 12 16 20 24 28 32 36 40
Volu m e o f N a O H (a q ) / cm – 3

(i) Explain why the temperature reaches a maximum and then falls slightly on
addition of further sodium hydroxide solution.
………….……………….……………………………………………………..
………….……………….……………………………………………………..
………….……………….……………………………………………………..
(2)

(ii) From the graph, what volume of the aqueous sodium hydroxide was required
for complete reaction?
………….……………….……………………………………………………..
(1)

(iii) Calculate the amount (number of moles) of sodium hydroxide in this volume
of solution.

(1)

(iv) Calculate the amount (number of moles) of copper ions that have reacted.

(1)

(v) Write the ratio of moles of copper ions to hydroxide ions reacting.

(1)

(vi) Write the formula of the copper hydroxide that is produced.

http://www.epingsoft.com
Generated by Direct DocX to Doc

(1)

http://www.epingsoft.com
Generated by Direct DocX to Doc

(b) The data call be used to find the enthalpy change for the reaction between sodium
hydroxide and the copper salt.

(i) Use the graph to find the temperature rise that occurs for complete reaction.
………….……………….……………………………………………………..
(1)

(ii) Find the heat change, q, that occurs in the polystyrene cup for complete reaction.
Use the formula

q = 168 × T joules

(1)

(iii) Use your results from (a)(iv) and (b)(ii) above, to find the molar enthalpy
change, H, for the reaction. Give the correct sign and units to the answer.

(3)

………………...……………….……………………………………………………..

………………...……………….……………………………………………………..
(2)
(Total 14 marks)

12. An excess of zinc powder was added to 20.0 cm3 of a solution of copper(II) sulphate of
concentration 0.500 mol dm–3. The temperature increased by 26.3 °C.

(a) How many moles of copper(II) sulphate were used in this experiment?

(1)
(b) Calculate the enthalpy change, ΔH, in kJ mol–1 for this reaction given that:

specific  mass of  temperature

energy change =
heat capacity solution change
/J /J g1 K1 /g /K
Assume that the mass of solution is 20.0 g and the specific heat capacity of the solution
is 4.18 J g–1K–1.

http://www.epingsoft.com
Generated by Direct DocX to Doc

(2)
(Total 5 marks)

13. Urea, which is used as a fertillser in much of mainland Europe, Asia and Africa, is
manufactured by the reaction of ammonia and carbon dioxide.

2NH3(g) + CO2(g)  NH2CONH2(s) + H2O(l)

(a) Define the term standard enthalpy of formation, Hf , of urea.

...............................................................................................................................

...............................................................................................................................
(3)
(b) Calculate the enthalpy change, H for the reaction above, given the following
standard enthalpies of formation.

Substance Hf / kJ mol–1

NH3(g) –46.2
CO2(g) –393.5
NH2CONH2(s) –632.2
H2O(l) –285.8

(3)
(Total 6 marks)

14. (a) Halogenoalkanes react with many nucleophiles.

Define the term nucleophile.

...............................................................................................................................

http://www.epingsoft.com
Generated by Direct DocX to Doc

...............................................................................................................................
(2)
(b) (i) Identify the reagent and conditions necessary for the conversion of iodoethane to
ethylamine, C2H5NH2.
Reagent:.........................................................................................................
Conditions:.....................................................................................................
......................................................................................................................
(3)

(ii) State why the rate of reaction would be slower if bromobutane were used in place
of iodoethane, with all other conditions remaining the same.
......................................................................................................................
......................................................................................................................
(1)

(c) Iodoethane reacts with water to form ethanol and hydrogen iodide.
C2H5I + H2O  C2H5OH + HI Hf = +36 kJ mol–1
Use some or all of the data below to calculate the CI bond enthalpy.

Bond enthalpy Bond enthalpy

Bond Bond
/ kJ mol–1 / kJ mol–1
CH 413 HI 298
CC 347 CO 358
HO 464

(3)

(d) Ethanol was heated under reflux with an excess of a mixture of potassium
dichromate(VI) and dilute sulphuric acid. Draw the full structural formnula of the
organic product.

(1)
(Total 10 marks)

15. (a) The equation below shows the reaction which occurs when ammonia is dissolved in water.


NH3(g) + H2O(1) NH 4 (aq) + OH–(aq)

http://www.epingsoft.com
Generated by Direct DocX to Doc

(i) Explain why water is classified as an acid in this reaction.

..........................................................................................................................

..........................................................................................................................
(1)

(ii) The ammonia is acting as a weak base in this reaction.

What is the difference between a weak base and a strong base?

..........................................................................................................................

..........................................................................................................................
(1)

(b) Ammonia reacts with oxygen to form the gases nitrogen(II) oxide and steam.

(i) Complete the Hess cycle below so that ΔHreaction can be calculated using standard
enthalpy changes of formation. Include state symbols.

(2)

(ii) Calculate ΔHreaction for this reaction using the following data.

ΔHf [NH3(g)] = – 46.1 kJ mol–1

ΔHf [NO(g)] = + 90.2 kJ mol–1

ΔHf [H2O(g)] = – 241.8 kJ mol–1

Include a sign and units in your answer and give your answer to three significant
figures.

(3)
(Total 7 marks)

16. The apparatus shown in the diagram below may be used to find the enthalpy of combustion of
alcohols.

http://www.epingsoft.com
Generated by Direct DocX to Doc

w ater

sp irit lam p +
eth an o l

Using the apparatus, a student recorded the results included in the table below.

Alcohol = ethanol, C2H5OH

Molar Mass (C2H5OH) = 46.0 g mol–1
Volume of water in beaker = 200 cm3
 mass of water in beaker = 200 g
Weighings
Spirit lamp + ethanol before combustion =
198.76 g
Spirit lamp + ethanol after combustion = 197.68
g
Temperatures
Water before heating = 19.5 C
Water after heating = 38.1 C
Specific heat capacity of water = 4.18 J g–1 C–1

(a) What assumption is the student making about water to be able to state that its mass is
numerically equal to its volume?

.........................................................................................................................................
......
(1)

(b) Calculate the heat gained by the water. Give your answer in kJ.

(2)

(c) Calculate the amount (number of moles) of ethanol used.

(2)

http://www.epingsoft.com
Generated by Direct DocX to Doc

(d) Using your values from (b) and (c), calculate the enthalpy of combustion of ethanol.
Give your answer to a number of significant figures consistent with the readings in
the table. Include a sign and units in your answer.

(3)
(e) The student’s evaluation of the experiment is given below.

My calculated value of the enthalpy of combustion was

numerically much less than the data
book value. The
reasons for my low value include:
1 heat losses to the surrounding air;
2 when I re-checked the mass of the spirit lamp and
ethanol after combustion, I noticed that it had lost
mass even when it was not being used;
3 a black solid which formed on the base of the beaker.

http://www.epingsoft.com
Generated by Direct DocX to Doc

(i) Explain why the spirit lamp and ethanol lost mass even when not in use.

...............................................................................................................................
......

...............................................................................................................................
......
(1)

(ii) Suggest the identity of the black solid. Explain why its formation will lead to a
low value for the enthalpy of combustion.

Identity ..................................................................................................................
......

Explanation ...........................................................................................................
.....

...............................................................................................................................
......
(2)
(Total 11 marks)

17. This question is about a self-heating can of coffee.

The bottom of the can has a compartment containing copper(II) nitrate solution. When a button
on the bottom of the can is pressed, magnesium powder is released into the compartment
where it reacts with the copper(II) nitrate solution.

(a) (i) Write an ionic equation for the reaction between magnesium powder and copper(II)
ions. Include state symbols, but omit any spectator ions.

(2)

(ii) Show how the standard enthalpy change for this reaction could be calculated from
the standard enthalpies of formation of copper(II) ions and magnesium ions.
You should include a Hess cycle in your answer.

(3)

(b) The can contains 150 g of a solution of coffee in water.

The temperature of the solution needs to increase by 60 °C to produce a hot drink.

(i) Calculate the energy change needed to produce a temperature increase of 60 °C in

the coffee, using the relationship

Energy change = 4.2 × mass of solution × temperature change.

http://www.epingsoft.com
Generated by Direct DocX to Doc

Remember to include a unit in your answer.

(2)

(ii) The standard enthalpy change for this reaction is –530 kJ mol–1.

Calculate the number of moles of reactants needed to produce the energy change in
(i).

(1)

(iii) A solution of copper(II) nitrate of concentration 8.0 mol dm–3 is used.

Use your answer to (ii) to calculate the volume, in cm3, of copper(II) nitrate solution
needed.

Your answer should be given to two significant figures.

(1)

....................................................................................................................................

....................................................................................................................................
(2)
(Total 11 marks)

18. The reaction between chlorine and methane, in the presence of ultraviolet light, involves the
formation of free radicals and includes the following steps:

A Cl2  2Cl• ΔΗο = +242 kJ mol–1

B CH4 + Cl•  HCl + CH3• ΔΗο = +4 kJ mol–1

C Cl2 + CH3•  CH3Cl + Cl• ΔΗο = –97 kJ mol–1

D Cl• + Cl•  Cl2

E CH3• + CH3•  CH3CH3

http://www.epingsoft.com
Generated by Direct DocX to Doc

F Cl• + CH3•  CH3Cl ΔΗο = –339 kJ mol–1

(a) (i) What is meant by a free radical? ....................................................................

(ii) Draw a ‘dot-and-cross’ diagram, showing outer shell electrons only, for a
chlorine free radical.

(1)

(iii) What type of bond breaking occurs in step A?

...........................................................................................................................
(1)

(b) Which of the steps, A to F, are chain propagation steps?

...........................................................................................................................
(1)

(1)

(ii) Calculate the standard enthalpy change, ΔΗο, for this reaction.

(2)

http://www.epingsoft.com
Generated by Direct DocX to Doc

(d) (i) What is the value of ΔΗο for step D? ................................................................

(1)

(ii) Would you expect step E to be exothermic or endothermic? Justify your answer.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(1)

(e) The overall reaction was repeated using bromine gas instead of chlorine gas.

Would you expect step A for bromine to be more or less endothermic than step A for
chlorine? Justify your answer.

....................................................................................................................................

....................................................................................................................................
(2)
(Total 11 marks)

19. In two similar, separate experiments the enthalpy changes for the reactions of sodium
hydrogencarbonate and sodium carbonate with excess dilute hydrochloric acid were
determined.

(a) The first experiment was to find the enthalpy change, H1, for the reaction
NaHCO3(s) + HCl(aq)  NaCl(aq) + CO2(g) + H2O(l)

Measurement Reading
Mass of solid sodium hydrogencarbonate added to
5.00 g
hydrochloric acid.

Volume of hydrochloric acid 50.0 cm3

Temperature of hydrochloric acid before addition

22.0 C
of solid sodium hydrogencarbonate

Final temperature of solution 15.5 C

Molar mass of sodium hydrogencarbonate 84.0 g mol–1

Specific heat capacity of solution 4.18 J g–1 C–1

(i) Calculate the amount (moles) of sodium hydrogencarbonate used.

http://www.epingsoft.com
Generated by Direct DocX to Doc

(1)

(ii) Calculate the heat absorbed in the reaction in kJ.

[Assume that 1 cm3 of solution has a mass of 1 g]

(2)

(iii) Calculate the value of H1 in kJ mol–1. Include a sign in your answer expressing
it to a number of significant figures suggested by the data in the table.

(2)

(b) In the second experiment the enthalpy change for the reaction between sodium
carbonate and dilute hydrochloric acid was measured.

Na2CO3(s) + 2HCl (aq)  2NaCI(aq) + CO2(g) + H2O(l)

The molar enthalpy change, H2, was calculated to be –35.6 kJ mol–1

(i) Give TWO ways in which the temperature change differs when equal molar
amounts of sodium hydrogencarbonate and sodium carbonate react separately
with the same volume of hydrochloric acid.

...............................................................................................................................
......

...............................................................................................................................
......
(2)

(ii) Give ONE assumption that has been made in calculating the values of H1, and
H2 from experimental results.

...............................................................................................................................
......

http://www.epingsoft.com
Generated by Direct DocX to Doc

...............................................................................................................................
......
(1)
(Total 8 marks)

20. In the manufacture of beer, brewers often add small amounts of salts of Group 2 elements to
the water used. These salts influence the chemical reactions during the brewing process.
Two such salts are calcium sulphate and magnesium sulphate.

(a) A flame test can be used to confirm that a sample of a salt contains calcium ions.

(i) Describe how you would carry out a flame test.

............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
(3)

(ii) A positive test results in a brick-red flame colour. Describe the changes that occur
in calcium ions to produce a colour.
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
(2)

(iii) Impurities in the salt may lead to other colours being observed in the flame.
What metal ion is likely to be present if a yellow flame is seen?
............................................................................................................................
(1)

(b) Magnesium sulphate can be used in its anhydrous form, MgSO4(s), or in its hydrated
form, MgSO4.7H2O(s).

An experiment was carried out to find the enthalpy change when hydrated magnesium
sulphate dissolved completely in water.
excess water
MgSO4.7H2O(s)        MgSO4(aq) + 7H2O(l)

12.3 g of hydrated magnesium sulphate was added to 100 g of water in a simple calorimeter
and the temperature was found to fall by 1.1 °C.

(i) Calculate the energy change, in joules, that occurred in the experiment, using the
relationship

Energy change (J) = 4.18 × mass of water × temperature change

http://www.epingsoft.com
Generated by Direct DocX to Doc

(2)

(ii) Calculate the number of moles of hydrated magnesium sulphate used in the
experiment. Use the Periodic Table as a source of data.

(2)

(iii) Use your answers to (i) and (ii) to calculate the enthalpy change for the reaction.
Include a sign and units in your final answer, which should be given to 2
significant figures.

(2)

http://www.epingsoft.com
Generated by Direct DocX to Doc

(c) The enthalpy change as hydrated magnesium sulphate is converted to anhydrous

magnesium sulphate is very difficult to measure. The Hess Cycle below can be used
to find this enthalpy change, ΔHr.

(i) Use the cycle to write an expression for ΔHr using ΔH1 and ΔH2.

(1)

(ii) Use your expression in (c)(i) and your answer from (b)(iii) to calculate ΔHr.

Include a sign and units in your final answer, which should be given to 2 significant
figures.

(2)
(Total 15 marks)

21. Phosphine, PH3, is a hydride of the Group 5 element, phosphorus.

(a) (i) Draw a ‘dot-and-cross’ diagram of a phosphine molecule. You should include only
outer shell electrons.

(1)

(ii) Draw the shape you would expect for the phosphine molecule, suggesting a value
for the HPH bond angle.

HPH bond
angle .......................................................................................................
(2)

(iii) Explain the shape of the phosphine molecule you have given in your answer in
(ii).

Justify your value for the HPH bond angle.

http://www.epingsoft.com
Generated by Direct DocX to Doc

.............................................................................................................................
(2)

(b) (i) Write a balanced equation, including state symbols, for the atomisation of phosphine
gas.
.............................................................................................................................
(1)

(ii) Use your answer to (i) and the data below to calculate the standard enthalpy
change of atomisation of phosphine at 298 K. Include a sign and units in your
answer.
ΔHοf[PH3(g)] = + 5.4 kJ mol1
ΔHοat[½H2(g)] = + 218.0 kJ mol1
ΔHοat[P(s)] = + 314.6 kJ mol1

(3)

(iii) Calculate a value for the bond energy of the bond between phosphorus and
hydrogen, using your answer to (ii).

(1)
(Total 10 marks)

22. Methane, CH4, is used as a domestic and industrial fuel and as a reagent in the petrochemical
industry.

(a) Define the term standard enthalpy of combustion.

.......................................................................................................................................

.......................................................................................................................................
(3)

(b) Methane burns in oxygen according to the equation:

H C H (g ) + 2 O O (g ) O C O (g ) + 2 H O H (g )

H
Use the average bond enthalpy data shown below to calculate the enthalpy change of this
reaction.

Bond Bond enthalpy/kJ mol–1

http://www.epingsoft.com
Generated by Direct DocX to Doc

CH +435
O==O +498
C==O +805
HO +464

(3)

(e) Methane is the feedstock in the manufacture of hydrogen according to the equation:

CH4(g) + 2H2O(g)  CO2(g) + 4H2(g)

Given the enthalpy of formation data below, draw a labelled Hess’s law cycle and use it to
calculate the enthalpy change of this reaction.

Substance Enthalpy of formation/kJ mol–1

CH4(g) –75
CO2(g) –394
H2O(g) –242

(4)
(Total 10 marks)

23. In an experiment to find the enthalpy of neutralisation of a monobasic acid, HX, with an
alkali, the following procedure was followed:

Step 1 25.0 cm3 of 1.00 mol dm–3 dilute aqueous acid, HX, was measured into a
polystyrene cup.

Step II A 0-100 °C thermometer was placed in the acid. The temperature of the acid was
immediately read and recorded.

Step III 5.00 cm3 portions of aqueous sodium hydroxide were added to the acid from a
burette. After each addition, the temperature of the solution was read and
recorded. The thermometer was removed and rinsed with water between each
addition. A total of 50.0 cm3 of aqueous sodium hydroxide was added.

(a) Suggest ONE change that could be made at Step II and ONE change that could be
made at Step III to improve the accuracy of the experiment.

http://www.epingsoft.com
Generated by Direct DocX to Doc

Step
II ...........................................................................................................................
........

.........................................................................................................................................
......

Step
III .........................................................................................................................
........

.........................................................................................................................................
......
(2)

(b) The readings of temperature and volume are plotted on the grid. Draw two separate
straight lines of best fit, extending the two lines so that they intersect.

×
×
× × ×
Tem p eratu re ×
/°C
×
×

20
×

15
0 10 20 30 40 50
Vo lu m e o f so d iu m h y d ro x id e ad d ed / cm 3
(2)

(c) From the graph, read off the maximum temperature rise, T, and the volume of aqueous
sodium hydroxide added at neutralisation, VN.

T = ..................................... C VN = ................................ cm3

(2)

(d) (i) Use the formula below to calculate the heat evolved in the neutralisation.

http://www.epingsoft.com
Generated by Direct DocX to Doc

VN  25T 4.18

Heat evolved = 1000 kJ

(1)

(ii) Given that the amount (moles) of acid neutralised was 0.025 mol, calculate the
enthalpy of neutralisation, Hneut, in units of kJ mol–1.

Hneut = ............................... kJ mol–1

(2)
(Total 9 marks)

24. A reaction of ammonium dichromate(VI) is shown by the following equation.

heat
(NH4)2Cr2O7(s)     N2(g) + 4H2O(g) + Cr2O3(s)

(a) What type of reaction is this?

......................................................................................................................................
(1)

(b) The enthalpy change for this reaction can be calculated from standard enthalpy changes
of formation.

(i) State fully what is meant by the standard enthalpy change of formation, ΔHfο,
of a compound.

...............................................................................................................................

...............................................................................................................................
(3)

(ii) Complete the Hess cycle for the reaction so that you can calculate the enthalpy
change of the reaction from standard enthalpy changes of formation.

http://www.epingsoft.com
Generated by Direct DocX to Doc

(3)

(iii) What is the value of ΔHfο[N2(g)]? ......................................................................

(1)

(iv) Calculate ΔHοr for the reaction using the following data. Remember to include a
sign and units in your answer.

ΔHfο[(NH4)2Cr2O7(s)] = –1810 kJ mol–1

ΔHfο[H2O(g)] = –242 kJ mol–1

ΔHfο[Cr2O3(s)] = –1140 kJ mol–1

(3)

(c) In this reaction, water vapour is formed which condenses to liquid water on cooling.
Is this reaction H2O(g)  H2O(l) exothermic or endothermic?

Justify your answer.

......................................................................................................................................

......................................................................................................................................
(2)
(Total 13 marks)

25. Chlorine can be converted to the gas chlorine(I) oxide, Cl2O.

http://www.epingsoft.com
Generated by Direct DocX to Doc

The standard molar enthalpy change of formation of chlorine(I) oxide and the standard molar
enthalpy changes of atomisation of chlorine and oxygen are given belo

ΔHfο [Cl2O(g)] = + 80.3 kJ mol–1

ΔHatο [½Cl2(g)] = +121.7 kJ mol–1

ΔHatο [½O2(g)] = +249.2 kJ mol–1

A partially completed Hess cycle involving chlorine(I) oxide is shown belo

(i) Insert the appropriate formulae, showing the correct quantities of each element, into the
box above. Include state symbols in your answer.
(1)

(ii) Insert arrows between the boxes, writing the correct numerical data alongside the
appropriate arrows.
(1)

(iii) Use the cycle to calculate ΔHatο [Cl2O(g)].

(1)

(iv) Calculate the Cl—O bond energy in chlorine(I) oxide.

(1)
(Total 14 marks)

26. (a) Enthalpy changes can be calculated using average bond enthalpy data.

(i) The enthalpy change to convert methane into gaseous atoms is shown below.

CH4(g) → C(g) + 4H(g) ∆H = +1664 kJ mol–1

Calculate the average bond enthalpy of a C—H bond in methane.

(1)

http://www.epingsoft.com
Generated by Direct DocX to Doc

(ii) Use the data in the table below and your answer to (a)(i) to calculate the enthalpy
change for
2C(g) + 2H2(g) + Br2(g) → CH2BrCH2Br(g)

Average bond Average bond

Bond enthalpy / kJ mol–1 Bond enthalpy / kJ mol–1
C—C +348 H—H +436
Br—Br +193 C—Br +276

(3)

(b) The standard enthalpy of formation of 1,2-dibromoethane, CH2BrCH2Br, is

–37.8 kJ mol–1.

Suggest the main reason for the difference between this value and your calculated value in
(a)(ii).

......................................................................................................................................

......................................................................................................................................
(1)
(Total 5 marks)

27. In an experiment to find the enthalpy change for the reaction

Zn(s) + Cu2+(aq)  Zn2+(aq) + Cu(s)

a student was given the following list of instructions:

 weigh out 5.0 g of zinc powder into a weighing bottle

 use a measuring cylinder to transfer 50 cm3 of 1.0 mol dm–3 aqueous copper(II) sulphate
into a polystyrene cup, firmly held in a 250 cm3 beaker

 stir the solution with the thermometer and record the temperature to the nearest 0.5 °C

 continue to stir the solution, recording its temperature every minute

http://www.epingsoft.com
Generated by Direct DocX to Doc

 at exactly 3.5 minutes, add the zinc powder to the aqueous copper(II) sulphate, stirring
continuously

 record the temperature of the solution every minute from 4.0 to 9.0 minutes.
The temperature readings obtained are shown in the table below.

Time/min 0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0
Temperature/°C 20.0 20.0 20.0 20.0 63.0 60.5 59.0 57.0 55.5 53.0

(a) (i) Plot a graph of temperature against time on the grid below.
7 0 .0

6 0 .0

5 0 .0

Tem p eratu re
/ ºC
4 0 .0

3 0 .0

2 0 .0

1 0 .0

0
0 1 .0 2 .0 3 .0 4 .0 5 .0 6 .0 7 .0 8 .0 9 .0 1 0 .0
Tim e / m in u tes
(2)

(ii) Use the graph to calculate the maximum temperature change, T. Show clearly
on the graph how you obtained your answer.

T = ................................................°C
(2)

http://www.epingsoft.com
Generated by Direct DocX to Doc

(iii) Give ONE reason why a series of temperature readings is obtained instead of just
the starting and maximum temperatures.

............................................................................................................................

............................................................................................................................
(1)

(b) (i) Calculate the heat change, in joules.

The specific heat capacity of the solution is 4.18 J g–1 °C–1.

(1)

(ii) What assumption have you made about the solution in your calculation in (i)?

............................................................................................................................

............................................................................................................................
(1)

(iii) Calculate the amount (moles) of copper (II) sulphate, CuSO4, in 50 cm3 of a
1.0 mol dm–3 solution.

(1)

(iv) Calculate the enthalpy change for this reaction in kJ mol–1.

(2)

Give a reason for each.

Improvement 1 ............................................................................................................

......................................................................................................................................

Reason .........................................................................................................................

......................................................................................................................................
http://www.epingsoft.com
Generated by Direct DocX to Doc

......................................................................................................................................

Improvement 2 ............................................................................................................

......................................................................................................................................

Reason ..........................................................................................................................

......................................................................................................................................

......................................................................................................................................
(4)
(Total 14 marks)

28. The values of the lattice energies of potassium iodide and calcium iodide experimentally
determined from Born-Haber cycles and theoretically calculated from an ionic model
are shown below.

Experimental lattice Theoretical

energy lattice energy
/kJ mol–1 /kJ mol–1
Potassium iodide, KI(s) – 651 – 636
Calcium iodide, CaI2(s) –2074 –1905

(i) Explain why the experimental lattice energy of potassium iodide is less exothermic than
the experimental lattice energy of calcium iodide.

.....................................................................................................................................

.....................................................................................................................................
(3)

(ii) Explain why the experimental and theoretical values of the lattice energy are almost the
same for potassium iodide, but are significantly different for calcium iodide.

.....................................................................................................................................

http://www.epingsoft.com
Generated by Direct DocX to Doc

.....................................................................................................................................

.....................................................................................................................................
(3)
(Total 6 marks)

29. When solutions of potassium carbonate and calcium chloride are mixed together, the
following reaction takes place

CaCl2(aq) + K2CO3(aq) → CaCO3(s) + 2KCl(aq)

(a) Re-write the above equation as an ionic equation. Include state symbols, but omit any
spectator ions.

(2)

(b) An experiment was carried out to measure the enthalpy change for this reaction. 50 cm 3
of a 1.00 mol dm–3 solution of potassium carbonate was added to 50 cm3 of a
1.00 mol dm–3 solution of calcium chloride. The temperature fell by 1.5 °C.

(i) Calculate the energy taken in from the surroundings using the relationship

energy = mass of × specific heat capacity × temperature

solution of solution change
/J /g /J g–1 °C–1 /°C

You may assume that

 1.0 cm3 of solution has a mass of 1.0 g.
 The specific heat capacity of the solution is 4.2 J g–1 °C–1.

Energy taken in = .................... J

(1)

(ii) How many moles of calcium chloride are used in this experiment?

http://www.epingsoft.com
Generated by Direct DocX to Doc

(1)

(iii) Calculate the enthalpy change for the reaction, giving your answer to two
significant figures. Include a sign and units in your answer.

(2)

(iv) Which measurement is likely to have caused the major source of error in this
experiment? Explain your answer.

...............................................................................................................................
.

...............................................................................................................................
.
(1)

(v) What apparatus should be used to contain the reaction mixture during this
experiment?

...............................................................................................................................
.
(1)

(c) If the experiment in (b) was repeated, but using only 25 cm3 of each solution, predict
what the fall in temperature would be.

.......................................................................................................................................
(1)
(Total 9 marks)

30. (a) State Hess’s Law.

.....................................................................................................................................

.....................................................................................................................................
(2)

(b) Methane burns in oxygen.

http://www.epingsoft.com
Generated by Direct DocX to Doc

CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)

(i) Calculate the enthalpy change for this reaction, using the bond enthalpies
given below.

Bond enthalpy
/ kJ mol–1
C–H +435
O=O +498
C=O +805
H–O +464
(3)

(ii) State the name of this enthalpy change.

...........................................................................................................................
(1)

(iii) The value of this enthalpy change, under standard conditions, is –890 kJ mol–1.
State the meaning of standard conditions.

...........................................................................................................................

...........................................................................................................................
(2)

(iv) Suggest, with a reason, why the enthalpy change calculated in (i) is different
from the standard value quoted in (iii).

...........................................................................................................................

...........................................................................................................................
(2)

Use these facts to explain the difference between thermodynamic and kinetic stability.

.....................................................................................................................................

.....................................................................................................................................
http://www.epingsoft.com
Generated by Direct DocX to Doc

.....................................................................................................................................

.....................................................................................................................................
(4)
(Total 14 marks)

31. A student carried out an experiment to find the concentration of a solution of nitric acid and
also its enthalpy of neutralisation.

• The solutions of nitric acid and sodium hydroxide were allowed to reach the same temperature.
• 50.0 cm3 of the nitric acid was pipetted into a polystyrene cup.
• A burette was filled with a solution of 2.0 mol dm3 sodium hydroxide, NaOH.
• The initial temperature of the acid was recorded.
• The sodium hydroxide was added to the acid in 5.0 cm3 portions.
• After each addition, the mixture was stirred and the maximum temperature recorded.
• This was repeated until 45 cm3 of the sodium hydroxide solution had been added.

The student plotted the results, as shown below.

http://www.epingsoft.com
Generated by Direct DocX to Doc

26
Tem p eratu re
/°C

16
0 5 10 15 20 25 30 35 40 45 50
Vo lu m e o f 2 .0 m o l d m – 3 so d iu m h y d ro x id e so lu tio n ad d ed / cm 3

(a) Complete the graph by drawing two intersecting straight lines of best fit.
(1)

(b) The point where the lines cross represents the neutralisation of the nitric acid by the
sodium hydroxide solution.

Use the graph to find:

(i) the volume of 2.0 mol dm3 sodium hydroxide solution, NaOH, that reacts exactly
with the 50 cm3 of the nitric acid.

...........................................................................................................................
(1)

(ii) the maximum temperature change, T, in the reaction.

...........................................................................................................................
(1)
http://www.epingsoft.com
Generated by Direct DocX to Doc

NaOH(aq) + HNO3(aq)  NaNO3(aq) + H2O(l)

(i) Calculate the amount (moles) of sodium hydroxide used to neutralise the 50 cm 3
of nitric acid.

(1)

(ii) Write the amount (moles) of nitric acid in 50.0 cm3 of the solution.

...........................................................................................................................
(1)

(iii) Hence calculate the concentration of nitric acid, HNO 3, in mol dm3.

(2)

http://www.epingsoft.com
Generated by Direct DocX to Doc

(d) (i) Use the data from (b) to calculate the heat change for this reaction.

The density of the mixture produced at neutralisation is 1.0g cm–3 and the specific
heat capacity of the mixture is 4.2 J g–1 °C–1.

Heat change = mass × specific heat capacity × T

(2)

(ii) Use your answer from (d)(i) and (c)(iii) to calculate the enthalpy of neutralisation
per mole of nitric acid, HNO3. Include a sign and units with your answer.

(3)

(e) The enthalpy of neutralisation found by this method may be less exothermic than the
data book value because of heat loss.

Suggest ONE way to reduce the error due to heat loss.

.....................................................................................................................................

.....................................................................................................................................
(1)
(Total 13 marks)

32. (a) Calculate the number of atoms in 3.50 g of lithium.

Use the Periodic Table as a source of data.

[The Avogadro constant, L = 6.02 × 1023 mol–1]

(2)

(b) The equation for the reaction of lithium with hydrochloric acid is shown below.

2Li(s) + 2HCl(aq)  2LiCl(aq) + H2(g)

(i) Rewrite this equation as an ionic equation, omitting the spectator ions.

http://www.epingsoft.com
Generated by Direct DocX to Doc

(1)

(ii) Draw a ‘dot and cross’ diagram of lithium chloride showing all the electrons.
Indicate charges clearly on your diagram.

(2)

(iii) The value of the standard enthalpy change for the reaction, Hο, is –557 kJ mol–
1. State TWO of the reaction conditions necessary for this enthalpy change to
be standard.

...........................................................................................................................

...........................................................................................................................
(2)
(Total 7 marks)

33. (a) Define the term standard enthalpy of formation.

.....................................................................................................................................

.....................................................................................................................................
(3)

http://www.epingsoft.com
Generated by Direct DocX to Doc

(b) The dissociation of phosphorus pentachloride is a reversible reaction.

PCl5(g) PCl3(g) + Cl2(g)

(i) Use the values of enthalpy of formation given to calculate ∆H for the forward
reaction.
∆Hf /
kJ mol–1
PCl5(g) – 399
PCl3(g) – 306

(1)

(ii) Explain, with reasons, the effect that raising the temperature would have on the
composition of the equilibrium mixture.

...........................................................................................................................

...........................................................................................................................
(2)

(iii) Other than by changing the temperature, suggest how the amount of PCl5 present
at equilibrium could be increased. Give a reason for your answer.

...........................................................................................................................

...........................................................................................................................
(2)
(Total 8 marks)

34. The enthalpy change for the thermal decomposition of calcium carbonate cannot be measured
directly, but can be found by carrying out two reactions as shown in the Hess cycle below.
H reactio n
C aC O 3 (s) C aO (s) + C O 2 (g )

H 3 H 4

E lem en ts in th eir stan d ard states

http://www.epingsoft.com
Generated by Direct DocX to Doc

(a) Suggest ONE reason why it is difficult to measure  Hreaction directly by experiment.

.....................................................................................................................................

.....................................................................................................................................
(1)

(b) In an experiment to find  H1 a student added 2.00 g of finely powdered calcium

carbonate to 20.0 cm3 of 2.50 mol dm–3 hydrochloric acid solution (an excess) in a
polystyrene container. The temperature rose from 20.5 °C to 23.0 °C.

(i) Why is the calcium carbonate used in this experiment finely powdered, rather than
in lumps? Explain why this is important for an accurate result.

...........................................................................................................................

...........................................................................................................................
(2)

(ii) Calculate the energy change using the relationship below.

Energy change = 4.2 × mass of solution × temperature change
/J /J g–1 K–1 /g /K

Assume that the mass of the solution is 20 g.

(1)

(iii) Calculate the enthalpy change, H1. Include a sign and units in your answer.
[The molar mass of CaCO3 is 100 g mol–1]

(3)

http://www.epingsoft.com
Generated by Direct DocX to Doc

(iv) In another experiment, the value of  H2 was found to be –181 kJ mol–1.

Use this result and your answer to (iii) to calculate the value of  Hreaction.

(2)

(c) The student checked the experimental results using information from the Book of data
in another Hess cycle.
H reactio n
C aC O 3 (s) C aC O (s) + C O 2 (g )

H 3 H 4

E lem en ts in th eir stan d ard states

Name the enthalpy change represented by H3.

.....................................................................................................................................
(1)
(Total 10 marks)

35. The Hess cycle below can be used to estimate the enthalpy change of formation, Hf, of the
unstable gaseous compound with the formula HOCl(g).

H O C l(g ) + 6 6 7 k J m o l –1
G aseo u s ato m s o f th e elem en ts

H f + 5 8 9 k J m o l –1

E lem en ts in th eir stan d ard states

http://www.epingsoft.com
Generated by Direct DocX to Doc

(a) (i) Insert formulae, with state symbols, into the appropriate boxes, to show the correct
quantities of each element.
(1)

H f
(ii) Use the cycle to calculate a value for the enthalpy change of formation,
[HOCl(g)].

(1)

(iii) Assuming that the H—O bond energy is +464 kJ mol–1, calculate a value for the
O—Cl bond energy.

(1)

(b) (i) Draw a ‘dot and cross’ diagram for the HOCl molecule showing outer electrons only.

(2)

(ii) Predict the HOCl bond angle. Justify your answer.

Angle ................................................................................................................

Justification ......................................................................................................

...........................................................................................................................

...........................................................................................................................
(2)

http://www.epingsoft.com
Generated by Direct DocX to Doc

Cl2O(g) + H2O(g) 2HOCl(g)

What effect, if any, would an increase in pressure have on the proportion of HOCl(g) at
equilibrium? Justify your answer.

.....................................................................................................................................

.....................................................................................................................................
(2)
(Total 9 marks)

36. (a) Define the term standard enthalpy of formation.

.....................................................................................................................................

.....................................................................................................................................
(3)

(b) In the Haber process, ammonia is manufactured from nitrogen and hydrogen as shown
in the equation.

N2(g) + 3H2(g) 2NH3(g)

(i) Use the bond enthalpies below to calculate the standard enthalpy of formation
of ammonia.

Bond Bond enthalpy / kJ mol–1

N≡N in N2 +945
H–H in H2 +436
N–H in NH3 +391

(4)

(ii) Draw a labelled enthalpy level diagram for the formation of ammonia in the
Haber process.
http://www.epingsoft.com
Generated by Direct DocX to Doc

E n th alp y

(2)

(iii) State the temperature used in the Haber process and explain in terms of the rate
of reaction and position of equilibrium, why this temperature is chosen.

Temperature .......................

...........................................................................................................................

...........................................................................................................................
(3)

(iv) Identify the catalyst used in the Haber process and state what effect, if any, it has
on the equilibrium yield of ammonia.

Catalyst ................................................................

Effect on yield ...................................................................................................

(2)

(v) Explain why it is necessary to use a catalyst in this process.

...........................................................................................................................

http://www.epingsoft.com
Generated by Direct DocX to Doc

...........................................................................................................................

...........................................................................................................................
(1)

(c) The pressure used in the Haber process is 250 atmospheres.

(i) State and explain an advantage of increasing the pressure to 1000 atmospheres.

...........................................................................................................................

...........................................................................................................................
(2)

(ii) Suggest a disadvantage of using a pressure of 1000 atmospheres.

...........................................................................................................................

...........................................................................................................................
(1)
(Total 18 marks)

37. The enthalpy change for the reaction of anhydrous aluminium chloride, AlCl 3, with water can
be found as follows:

• Add about 100 cm3 of distilled water to a weighed polystyrene cup.

• Measure the steady temperature of the water.

• Add anhydrous aluminium chloride to the polystyrene cup, with stirring.

• Measure the highest temperature reached.

• Re-weigh the polystyrene cup and contents

Data
Mass of anhydrous aluminium chloride = 4.00 g
Mass of solution = 104 g
Initial temperature = 17.5 °C
Highest temperature reached = 43.5 °C
Specific heat capacity of the solution = 4.09 J g–1 °C–1

http://www.epingsoft.com
Generated by Direct DocX to Doc

(i) Calculate the heat change in this experiment.

(2)

(ii) Assuming that 100 cm3 of water is a large excess, calculate the enthalpy change, in
kJ mol–1, when one mole of aluminium chloride reacts. Include a sign and unit in
your answer.

(3)
(Total 5 marks)

38. (a) (i) Write the equation which represents the change occurring when the standard enthalpy of
atomisation of bromine is measured.

...........................................................................................................................
(2)

(ii) Define lattice energy.

...........................................................................................................................

...........................................................................................................................
(3)

(b) A Born-Haber cycle for the formation of magnesium chloride is shown below.

http://www.epingsoft.com
Generated by Direct DocX to Doc

M g 2 + (g ) + 2 C l(g ) + 2 e –

M g 2 + (g ) + C l 2 (g ) + 2 e – M g 2 + (g ) + 2 C l – (g )

M g + (g ) + C l 2 (g ) + e –

M g (g ) + C l 2 (g )

M g (s) + C l 2 (g )

M g C l 2 (s)

Value / kJ mol–1
Enthalpy of atomisation of magnesium +150
1st ionisation energy of magnesium +736
2nd ionisation energy of magnesium +1450
Enthalpy of atomisation of chlorine +122
Enthalpy of formation of magnesium chloride –642
Lattice energy of magnesium chloride –2526

The theoretically calculated value for the lattice energy of magnesium chloride is
–2326 kJ mol–1.

Explain, in terms of the bonding in magnesium chloride, why the experimentally

determined value of –2526 kJ mol–1 is significantly different from the theoretical
value.

.....................................................................................................................................

.....................................................................................................................................
(2)
(c) The table shows values for the lattice energies of the metal chlorides of some Group 2
metals.

http://www.epingsoft.com
Generated by Direct DocX to Doc

Group 2 metal
MgCl2 CaCl2 SrCl2 BaCl2
chloride
Lattice energy/
–2526 –2237 –2112 –2018
kJ mol–1

Explain why these lattice energies become less exothermic from MgCl 2 to BaCl2.

(3)
(Total 10 marks)

39. An experiment was carried out to find the enthalpy change for the reaction of zinc powder
with copper(II) sulphate solution.

Zn(s) + CuSO4(aq)  ZnSO4(aq) + Cu(s)

50cm3 of copper(II) sulphate solution, of concentration 1.0 mol dm–3, was put into a polystyrene
cup and the temperature of the solution measured. After one minute, 5.0 g of zinc powder
was added, the mixture stirred with a thermometer and the temperature measured every 30
s.

(a) (i) What is meant by a spectator ion?

...........................................................................................................................

...........................................................................................................................
(1)

(ii) Give the formula of the spectator ion in this reaction.

...........................................................................................................................
(1)

(iii) Write the equation for this reaction, omitting the spectator ion.

(1)

(b) How would you measure the 50 cm3 of copper(II) sulphate solution?

.....................................................................................................................................

.....................................................................................................................................
(1)

(c) Give TWO reasons why it is better to use a polystyrene cup, rather than a metal
container, to obtain more accurate results.

.....................................................................................................................................

.....................................................................................................................................
http://www.epingsoft.com
Generated by Direct DocX to Doc

.....................................................................................................................................

.....................................................................................................................................
(2)

http://www.epingsoft.com
Generated by Direct DocX to Doc

(d) Calculate the number of moles of each of the reactants and hence deduce which reactant
is completely used up.
Use the Periodic Table as a source of data.

Moles of zinc powder

Moles of copper(II) sulphate

Reactant used up .................................................................

(3)
(e) The following results were obtained.

Time /s 0 60 90 120 150 180 210

Temperature /°C 22 22 60 65 63 61 59

(i) On the graph paper below, plot the results of this experiment.

http://www.epingsoft.com
Generated by Direct DocX to Doc

Tem p eratu re
/ºC
40

0
0 40 80 120 160 200 240
Tim e / s
(2)

(ii) Explain the shape of your graph

...........................................................................................................................

...........................................................................................................................
(2)

http://www.epingsoft.com
Generated by Direct DocX to Doc

(iii) The maximum recorded temperature in this experiment was 65°C. Use your
graph to estimate a more accurate maximum temperature.

...........................................................................................................................
(1)

(f) (i) Calculate the energy change in this experiment using your answer to (e)(iii) and the
relationship

energy change = mass of × specific heat capacity × temperature rise

solution of solution
/J /g /J °C–1 g–1 /°C

You may assume that

• 1.0 cm3 of solution has a mass of 1.0 g

• The specific heat capacity of the solution is 4.2 J °C–1 g–1

(1)

(ii) Use your answers to (d) and (f)(i) to calculate ∆H for this reaction. Include a sign
and units in your answer.

(3)
(Total 18 marks)

40. This question is about some of the chemicals used in car engines and their reactions.

(a) Compound X, shown below, is one component of petrol.

H CH3 H H H

H— C— — C— — C— — C— — C— H

H CH3 H CH3 H

(i) Name X.

...........................................................................................................................
(1)

(ii) Give the empirical formula of X.

...........................................................................................................................
(1)

(iii) X can be made by cracking decane, C10H22.

http://www.epingsoft.com
Generated by Direct DocX to Doc

Assuming only one other product forms in a cracking reaction, deduce the molecular
formula of this other product.

(1)

(iv) What is the sign of the enthalpy change for the reaction in which decane is
cracked? Give a reason for your answer.

...........................................................................................................................

...........................................................................................................................
(1)

(v) If the air supply in a car engine is poor, there is not enough air for carbon dioxide
to be produced.

Use this information to suggest ONE possible equation for the combustion of X in
this engine. Use the molecular formula of X in your equation.

(2)

(b) When air enters a car engine, as well as the fuel burning, nitrogen and oxygen can react
to form nitrogen(II) oxide.

N2(g) + O2(g) 2NO(g) ΔH = + 180 kJ mol–1

(i) What, if any, is the effect on the percentage of nitrogen(II) oxide in an equilibrium
mixture of these three gases if the pressure and temperature are increased?
Explain your answers.

Increase in pressure

...........................................................................................................................

Increase in temperature

...........................................................................................................................

...........................................................................................................................
(2)

(ii) In a car exhaust pipe, nitrogen(II) oxide passes over a catalytic converter.
The following reaction occurs.

http://www.epingsoft.com
Generated by Direct DocX to Doc

2NO(g) + 2CO(g) → N2(g) + 2CO2(g) ΔH = –746 kJ mol–1

Explain why this reaction speeds up when the car engine has been running for a few
minutes.

...........................................................................................................................

...........................................................................................................................
(1)

http://www.epingsoft.com
Generated by Direct DocX to Doc

(iii) A textbook says “The catalytic converter converts the gases coming out of the
engine into less harmful ones”.

State, with a reason, which of the four gases in the equation in (ii) you consider to be
least harmful.

...........................................................................................................................

...........................................................................................................................
(1)

(iv) The diagram below shows the reaction profile for the change which occurs in the
catalytic converter.
E n erg y

2 N O (g ) + 2 C O (g )

N 2 (g ) + 2 C O 2 (g )

P ro g ress o f reactio n

On the diagram, show the activation energy, EA.

Add a line showing the reaction profile if no catalyst is present.

(2)
(Total 12 marks)

41. (a) Define the term standard enthalpy of combustion.

.....................................................................................................................................

.....................................................................................................................................
(3)
(b) The following standard enthalpies of combustion are needed to calculate the standard
enthalpy of formation of ethanol, C2H5OH.

Substance Standard enthalpy of

http://www.epingsoft.com
Generated by Direct DocX to Doc

combustion /kJ mol–1

carbon, C (s, graphite) –394
hydrogen, H2(g) –286
ethanol, C2H5OH (l) –1371

(i) Complete the Hess’s Law cycle by filling in the box and labelling the arrows with
the enthalpy changes.
 Hf
2 C (s) + 3 H 2 (g ) + 3 ½ O 2 (g ) C 2 H 5 O H (l) + 3 O 2 (g )

...........................
...........................
........................... ...........................

............................... + ...............................

(3)

(ii) Use your Hess’s Law cycle to calculate the standard enthalpy of formation of
ethanol.

(2)
(Total 8 marks)

42. The apparatus used and the recordings made by a student, carrying out an experiment to
determine the enthalpy of combustion of methanol, are shown below.

Diagram

th erm o m eter

b eak er

w ater

sp irit lam p
m eth an o l

Results

http://www.epingsoft.com
Generated by Direct DocX to Doc

Molar mass (methanol) = 32 g mol–1

Volume of water in beaker = 50 cm3
Mass of water in beaker = 50 g
Weighings
Spirit lamp + methanol before combustion = 163.78 g
Spirit lamp + methanol after combustion = 163.44 g
Temperatures
Water before heating = 22.0 °C
Water after heating = 43.5 °C
Specific heat capacity of water = 4.18 J g–1 °C–1

Observations

• When the spirit lamp was being weighed its mass was continually falling.

• A black substance formed on the bottom of the beaker as the methanol burned.

(a) (i) Calculate the amount (moles) of methanol, CH3OH, burned.

(2)

(ii) Calculate the heat gained by the water. Give your answer in kJ.

(2)

(iii) Use your values from (i) and (ii) to calculate the enthalpy of combustion of
methanol in kJ mol–1. Include a sign with your answer.

∆H = ........................................ kJ mol–1
(2)

(b) (i) The thermometer used in the experiment can be read to an accuracy of ±0.5 °C.
Calculate the percentage error in the temperature change.

(1)

(ii) Calculate the maximum temperature change that could have occurred during the
experiment.

http://www.epingsoft.com
Generated by Direct DocX to Doc

(1)

...........................................................................................................................

...........................................................................................................................
(1)

(ii) Suggest the identity of the black substance that forms on the beaker. State the
effect on the value of the enthalpy of combustion obtained.

...........................................................................................................................

...........................................................................................................................
(2)
(Total 11 marks)

43. (a) An incomplete Born-Haber cycle for the formation of magnesium oxide, MgO, from its
constituent elements is shown below. All numerical values are in kJ mol–1.

H 3 = + 6 5 7

M g 2 + (g ) + O (g ) + 2 e –

en th alp y o f ato m isatio n

o f o x y g en = + 2 4 9

M g 2 + (g ) + 12 O 2 (g ) + 2 e –

first p lu s seco n d
io n isatio n en erg y o f lattice en erg y o f
m ag n esiu m = + 2 1 8 6 m ag n esiu m o x id e

M g (g ) + 12 O 2 (g )

H 2 = +150

M g (s) + 12 O 2 (g )

 H 1 = –602
M g O (s)

http://www.epingsoft.com
Generated by Direct DocX to Doc

(i) Complete the empty box on the cycle by writing in the formulae of the missing
species. State symbols are required.
(1)

(ii) Identify each of the following enthalpy changes by name:

ΔH1 ....................................................................................................................

ΔH2 ....................................................................................................................

ΔH3 ....................................................................................................................
(3)

(iii) Use the Born-Haber cycle to calculate the lattice energy of magnesium oxide.

(2)

(b) Magnesium iodide is another compound of magnesium. The radius of the magnesium
ion is 0.072 nm, whereas the radius of the iodide ion is much larger and is 0.215 nm.

(i) Describe the effect that the magnesium ion has on an iodide ion next to it in the
magnesium iodide lattice.

...........................................................................................................................

...........................................................................................................................
(1)

(ii) What TWO quantities must be known about the ions in a compound in order to
calculate a theoretical lattice energy?

...........................................................................................................................

...........................................................................................................................
(2)

(iii) Suggest how the value of the theoretical lattice energy would compare with the
experimental value from a Born-Haber Cycle for magnesium iodide.

Give a reason for your answer.

...........................................................................................................................

...........................................................................................................................
http://www.epingsoft.com
Generated by Direct DocX to Doc

...........................................................................................................................
(2)
(Total 11 marks)

44. Calcium hydroxide decomposes on strong heating to form calcium oxide and water.

Ca(OH)2(s) → CaO(s) + H2O(l)

Two samples of calcium hydroxide were taken, each weighing exactly 1.00 g.

The first sample was cautiously added to 25.0 cm3 of dilute hydrochloric acid contained in a glass
beaker. The temperature rise was measured and found to be 16.5 °C.

The other sample was heated for some time. It was then allowed to cool and then added to
another 25.0 cm3 portion of hydrochloric acid as before. In this case the temperature rose
by 25.5 °C.

In both cases, the acid used was an excess.

(a) (i) Calculate the energy produced by the reaction of each solid with the acid.

Use the relationship

Energy produced = mass of solution × 4.2 × temperature rise

/ J / g / J °C–1 g–1 /°C

You may assume that 1.0 cm3 of solution has a mass of 1.0 g. Ignore the mass of the
solid.

For the solid calcium hydroxide

For the solid calcium oxide

(1)

(ii) How many moles of calcium hydroxide were used in each experiment?
[Molar mass of Ca(OH)2 = 74.0 g mol–1]

(1)

(iii) Using your answers to (a)(i) and (ii), calculate the enthalpy changes for each
reaction.

Give your answers to two significant figures. Include the sign and units for each
answer.
http://www.epingsoft.com
Generated by Direct DocX to Doc

For the solid calcium hydroxide, ΔH1

For the solid calcium oxide, ΔH2

(2)

(b) A Hess cycle for all these reactions is shown below.

H reactio n
C a(O H ) 2 (s) C aO (s) + H 2 O (l)
2 H C l (aq ) 2 H C l (aq )

H 1 H 2

C aC l 2 (aq ) + 2 H 2 O (l)

(i) Use this Hess cycle and your answers in (a)(iii) to calculate ΔHreaction. Include a
sign and units.

(2)

(ii) Apart from the approximations involved in using the equation given in (a)(i), give
TWO other potential sources of error which are likely to affect the accuracy of
the results.

...........................................................................................................................

...........................................................................................................................
(2)

(iii) Suggest why ΔHreaction is difficult to determine directly by experiment.

...........................................................................................................................

...........................................................................................................................
(1)
(Total 9 marks)

http://www.epingsoft.com
Generated by Direct DocX to Doc

45. This question is about ammonia, NH3, which is produced as shown in the following equation.

N2(g) + 3H2(g) 2NH3(g)

(a) Use oxidation numbers to explain why this is a redox reaction.

.....................................................................................................................................

.....................................................................................................................................
(2)
(b) (i) Use the average (mean) bond enthalpy data to calculate a value for the enthalpy
change for this reaction. You are reminded to show all your working.

Average bond enthalpy

Bond
/ kJ mol–1
N≡N 944
H—H 436
N—H 388

(3)

(ii) The actual standard enthalpy change for this reaction is –92 kJ mol–1. Explain
why the value you calculated in (b)(i) is not the same as this.

...........................................................................................................................

...........................................................................................................................
(1)

(iii) At room temperature, a mixture of nitrogen and hydrogen is thermodynamically

unstable with respect to ammonia, but is kinetically stable.

Use the data in (b)(i) and (ii) to help you explain why this mixture is

thermodynamically unstable

...........................................................................................................................

...........................................................................................................................
http://www.epingsoft.com
Generated by Direct DocX to Doc

kinetically stable

...........................................................................................................................

...........................................................................................................................
(3)

(i) State and explain, in terms of collision theory, TWO ways to increase the rate of
the reaction. An increase in pressure does not alter the rate in this process.

...........................................................................................................................

...........................................................................................................................
(6)

(ii) State and explain TWO ways to increase the equilibrium yield of ammonia.

...........................................................................................................................

http://www.epingsoft.com
Generated by Direct DocX to Doc

...........................................................................................................................

...........................................................................................................................
(4)
(Total 19 marks)

46. The enthalpy change for the reaction between aqueous sodium hydroxide solution and
aqueous hydrochloric acid was determined by the following method:

• Aqueous hydrochloric acid was titrated against 25.0 cm3 of 1.50 mol dm–3 aqueous
sodium hydroxide solution using a suitable indicator. The mean (or average) titre was
22.75 cm3.

• 25.0 cm3 of the sodium hydroxide solution was carefully measured into a polystyrene cup
and 22.75 cm3 of the hydrochloric acid was transferred to a clean dry beaker.
Both solutions were allowed to stand for five minutes before their temperatures were
noted.

• The hydrochloric acid was then added to the sodium hydroxide solution, the mixture
stirred thoroughly and the highest temperature noted.

• The experiment was repeated three times giving an average temperature change of
+10.5°C.

(a) (i) Calculate the heat produced in the reaction, in joules.

Use the approximations that the density of the final solution is 1.00 g cm–3 and its
specific heat capacity is 4.18 J g–1 K–1.

(2)

(ii) Calculate the enthalpy change for the reaction, in kJ mol–1.

http://www.epingsoft.com
Generated by Direct DocX to Doc

(3)

(b) State ONE assumption made when calculating this enthalpy change, other than those
stated in (a)(i).

.....................................................................................................................................

.....................................................................................................................................
(1)
(Total 6 marks)

47. The Born-Haber cycle below represents the enthalpy changes when calcium hydride, CaH 2, is
formed from its elements.
C a 2 + (g ) + 2 e – + 2 H (g )

H 4 H 5

C a 2 + (g ) + 2 e – + H 2 (g ) C a 2 + (g ) + 2 H – (g )

H 3

C a (g ) + H 2 (g )

ΔH6
H 2

C a (s) + H 2 (g )

H 1

C aH 2 (s)

(a) Write down in terms of one of the symbols ΔH1 to ΔH6

(i) the lattice energy of calcium hydride ................................................................

(1)

(ii) the first electron affinity of hydrogen ................................................................

(1)

http://www.epingsoft.com
Generated by Direct DocX to Doc

(b) Use the data below to calculate the standard enthalpy of formation of calcium hydride,
CaH2(s).

value
/kJ mol–1
enthalpy of atomisation of calcium +178
first plus second ionisation energies of calcium +1735
enthalpy of atomisation of hydrogen +218
first electron affinity of hydrogen –73
lattice energy of calcium hydride –2389

Calculation:

(2)

(c) Explain why the lattice energy of magnesium hydride, MgH2(s), is more exothermic
than the lattice energy of calcium hydride, CaH2(s).

.....................................................................................................................................

.....................................................................................................................................
(3)
(Total 7 marks)

48. Two experiments were carried out in order to calculate the enthalpy change of formation of
magnesium carbonate, MgCO3.

A Hess cycle for these reactions is shown below.

http://www.epingsoft.com
Generated by Direct DocX to Doc

 Hf
Mg + C + O2 M g C O 3 (s)

E xp erim en t 1 + 2 H C l (aq )  H 1

 H3 + 2 H C l (aq ) E xp erim en t 2
M g C l 2 (aq ) + H 2 (g ) + C + O2

 H 2 = – 6 8 0 k J m o l–1

M g C l 2 (aq ) + H 2 O (l) + C O 2 (g )

(a) Complete the Hess cycle above for the formation of magnesium carbonate from its
elements by balancing the equations and adding state symbols.
(2)
(b) In Experiment 1 the temperature of 100 cm3 of hydrochloric acid was measured.
After one minute, 0.100 g of magnesium was added to the excess acid and the
temperature measured every minute. The following results were obtained:

Time / min 0 1 2 3 4 5 6
Temp / °C 21.0 21.0 25.3 25.1 24.9 24.8 24.7

(i) How many moles of magnesium were used in this experiment?

Use the Periodic Table as a source of data.

...........................................................................................................................
(1)

(ii) The initial concentration of the hydrochloric acid was 2.00 mol dm–3.

Calculate the number of moles of hydrochloric acid at the start and hence the number
remaining at the end of the experiment.

(3)

(iii) Plot the graph of temperature against time.

http://www.epingsoft.com
Generated by Direct DocX to Doc

(2)

(iv) Calculate the energy change in this experiment assuming the temperature rise is
4.5 °C. Use the expression

Energy change (J) = 4.2 × mass of solution × temperature change

[Assume that 1 cm3 of solution has a mass of 1 g]

(1)

(v) Use your answer to (iv) to calculate ∆H1 for one mole of magnesium reacting
with hydrochloric acid. Include a sign and units in your answer.

(2)

(vi) Suggest why a temperature rise of 4.5 °C was used in the calculation in (iv).

...........................................................................................................................

...........................................................................................................................
http://www.epingsoft.com
Generated by Direct DocX to Doc

(1)

The temperature changed from 21.0 °C to 23.5 °C resulting in an energy change of 1.05 kJ.

(i) Calculate the mass of one mole of magnesium carbonate, MgCO3 and hence the
number of moles of magnesium carbonate used in this experiment.
Use the Periodic Table as a source of data.

(2)

(ii) Using the method in part (b)(v), calculate ∆H3.

(1)

(d) Using your answers to (b)(v) and (c)(ii), calculate the enthalpy change of formation,
∆Hf, of magnesium carbonate, MgCO3.
Include a sign and units in your answer.

(2)

(e) Why is it impossible to measure ∆Hf of MgCO3(s) directly?

.....................................................................................................................................

.....................................................................................................................................
(1)
(Total 18 marks)

49. Calculate the standard enthalpy change of formation of gaseous silicon tetrachloride,
ΔHοf [SiCl4(g)].

Your answer should include a sign and units.

Use the Hess cycle below and the following data at 298 K.

H ato [Si(s)] = +455.6 kJ mol–1

H ato [½Cl2] = +121.7 kJ mol–1

http://www.epingsoft.com
Generated by Direct DocX to Doc

Bond energy, E (Si-Cl) = +407.4 kJ mol–1

H
S iC l 4 (g ) S i(g ) + 4 C l(g )

H f [S iC l 4 (g )]

S i(s) + 2 C l 2 (g )
(Total 3 marks)

50. An experiment was carried out to measure the enthalpy change for the reaction of zinc with
aqueous copper(II) sulphate.

The equation for the reaction is

Zn + CuSO4 → ZnSO4 + Cu

• A measuring cylinder was used to transfer separate 50 cm3 samples of 1.25 mol dm–3
copper(II) sulphate solution into polystyrene cups.

• Weighed amounts of zinc powder were added to each sample in turn.

• Each mixture was stirred thoroughly and the temperature rise noted with a thermometer
accurate to 0.5 °C.

The results of this experiment are summarised on the graph below.

7 0 .0
× × × × × ×
6 0 .0
×
5 0 .0
×

4 0 .0 ×
Tem p eratu re
ch an g e /º C ×
3 0 .0
×
2 0 .0
×
1 0 .0

0 .0 ×
0 .0 0 1 .0 0 2 .0 0 3 .0 0 4 .0 0 5 .0 0 6 .0 0 7 .0 0
M ass o f zin c / g

(a) Explain why the graph initially shows a rise in temperature and then levels off.

.....................................................................................................................................

http://www.epingsoft.com
Generated by Direct DocX to Doc

.....................................................................................................................................
(2)

(b) (i) Suggest why the mass of metal is not used in the calculation of the heat change.

...........................................................................................................................

...........................................................................................................................
(1)

(ii) The graph shows that the maximum temperature change is 63.5 °C. Use this value
to calculate the maximum heat change, in joules, in this reaction.

You should assume that the density of the solution is 1.00 g cm–3 and its heat
capacity is the same as water, 4.18 J g–1 °C–1.

(1)

(iii) From the heat change calculated in (b)(ii) calculate the enthalpy change, in kJ
mol–1, for the reaction. Include the appropriate sign and give your answer to
three significant figures.

(4)

(c) (i) It is suggested that the precision of the experiment would be improved by using a
thermometer accurate to 0.1 °C.

Explain why this suggestion is incorrect.

...........................................................................................................................

...........................................................................................................................
(1)

(ii) Suggest a simple practical change to the method that would make the experiment
more accurate.

...........................................................................................................................

http://www.epingsoft.com
Generated by Direct DocX to Doc

...........................................................................................................................

...........................................................................................................................
(1)
(Total 10 marks)

51. (a) The following data were collected to use in a Born-Haber cycle for silver fluoride, AgF.

Value
/kJ mol–1
enthalpy of atomisation of silver +285
first ionisation energy of silver +731
enthalpy of atomisation of fluorine +79
enthalpy of formation of silver fluoride –205
lattice energy of silver fluoride –958

On the following outline of a Born-Haber cycle, complete boxes A and B by adding the
formula and state symbol for the appropriate species. Write the name of the enthalpy
change at C.

A g + (g ) + F – (g ) A g F (s)

C ............................................
B ox B ox
A B ............................................

A g (s) + ½ F 2 (g )

(3)

(b) ΔHlatt (theoretical) is the lattice energy calculated assuming the crystal lattice is
completely ionic.
ΔHlatt (experimental) is the lattice energy determined experimentally using the Born-
Haber cycle.
Values for the silver halides are listed below.

ΔHlatt ΔHlatt ΔHlatt (theoretical)

(theoretical) (experimental) minus
Formula of halide
ΔHlatt (experimental)
/ kJ mol–1 / kJ mol–1 / kJ mol–1
AgF –920 –958 38
AgCl –833 –905 72
AgBr –816 –891 75
AgI –778 –889 111

http://www.epingsoft.com
Generated by Direct DocX to Doc

(i) Explain why the theoretical lattice energies become less exothermic from AgF to
AgI.

...........................................................................................................................

...........................................................................................................................
(3)

(ii) Explain why the values of the theoretical and experimental lattice energies are
different.

...........................................................................................................................

...........................................................................................................................
(2)

(iii) Explain why the difference between the theoretical and experimental lattice
energies increases from AgF to AgI.

...........................................................................................................................

...........................................................................................................................
(2)
(Total 10 marks)

52. The Hess cycle below can be used to find the enthalpy change, ∆Hr, for the reaction between
hydrogen sulphide and sulphur dioxide, using standard enthalpy changes of formation.
H r
S O 2 (g ) + 2 H 2 S (g ) 3 S (s) + 2 H 2 O (l)

H 1 H 2

http://www.epingsoft.com
Generated by Direct DocX to Doc

(i) Complete the cycle by filling in the empty box.

(2)

(ii) What is meant by the standard enthalpy change of formation, ∆Hfο, of a compound?

.....................................................................................................................................

.....................................................................................................................................
(3)
(iii) Use the cycle and the data below to calculate the enthalpy change of the reaction, ∆Hr.

∆Hfο / kJ mol–1
SO2 (g) –296.8
H2S (g) –20.6
H2O (l) –285.8
(2)
(Total 7 marks)

53. Which of the equations shown below represents the reaction for which H is the standard
enthalpy change of formation, Hοf 298, for ethanol, C2H5OH. Ethanol melts at 156 K and
boils at 352 K.

A 2C(g) + 6H(g) + O(g)  C2H5OH(g)

B 2C(s) + 3H2(g) + O2(g)  C2H5OH(l)

C 2C(s) + 3H2(g) + O(g)  C2H5OH(g)

D 2C(s) + 3H2(g) + ½O2(g)  C2H5OH(l)

(Total 1 mark)

54. Airbags, used as safety features in cars, contain sodium azide, NaN3. An airbag requires a
large volume of gas to be produced in a few milliseconds. The gas is produced in this
reaction:

2NaN3(s)  2Na(s) + 3N2(g) H is positive

When the airbag is fully inflated, 50 dm3 of nitrogen gas is produced.

(a) Calculate the number of molecules in 50 dm3 of nitrogen gas under these conditions.

[The Avogadro constant = 6.02 × 1023 mol–1. The molar volume of nitrogen gas under the
conditions in the airbag is 24 dm3 mol–1].

http://www.epingsoft.com
Generated by Direct DocX to Doc

(2)

(b) Calculate the mass of sodium azide, NaN3, that would produce 50 dm3 of nitrogen gas.

(3)

.....................................................................................................................................

.....................................................................................................................................
(1)

(d) The airbag must be strong enough not to burst in an accident. An airbag which has burst
in an accident is hazardous if the sodium azide in it has decomposed.

Explain why this is so.

.....................................................................................................................................

.....................................................................................................................................
(2)
(Total 8 marks)

55. A student investigated a reaction which could be used to warm up coffee in self-heating cans.

Mg(s) + Cu(NO3)2(aq)  Mg(NO3)2(aq) + Cu(s)

In the self-heating cans, the bottom has a compartment containing copper(II) nitrate solution.
When a button on the bottom of the can is pressed, the magnesium powder is released into
the compartment where it reacts with the copper(II) nitrate solution.

(a) A student investigated the enthalpy change for this reaction by measuring

50.0 cm3 of 0.300 mol dm–3 copper(II) nitrate solution into a 100 cm3 beaker and adding
1g (an excess) of magnesium powder.

The results are shown below.

Temperature of copper(II) nitrate solution at start = 22 °C

Temperature of mixture after reaction = 43 °C
http://www.epingsoft.com
Generated by Direct DocX to Doc

(i) Calculate the energy change which took place. The specific heat capacity of the
solution is 4.20 J g–1 K–1.

Which is the correct value for the energy change in joules?

(1)

(ii) How many moles of copper(II) nitrate were used in the experiment?

(1)

(iii) Calculate the enthalpy change for the reaction. You should include a sign and
units in your answer.

(2)

(iv) Suggest two changes you would make to the equipment used in order to improve
the accuracy of the result.

...........................................................................................................................

...........................................................................................................................
(2)

(b) The ionic equation for the reaction is shown belo

Mg(s) + Cu2+(aq)  Mg2+(aq) + Cu(s) H= –532 kJ mol–1

Would the following affect the value of the experimental result?

Explain your answer, stating the effect, if any, on the value of the enthalpy change
obtained.

(i) The student used 2 g rather than 1g of magnesium.

...........................................................................................................................

...........................................................................................................................
http://www.epingsoft.com
Generated by Direct DocX to Doc

(2)

(ii) The heat losses that occurred from the student’s beaker.

...........................................................................................................................

...........................................................................................................................
(2)

Suggest a change you could make to the mixture in the experiment in (a) to produce a
greater temperature rise. You are not expected to do a calculation.

.....................................................................................................................................

.....................................................................................................................................
(1)
(Total 11 marks)

56. The following data can be used in a Born-Haber cycle for copper(II) bromide, CuBr 2.

Enthalpy change of atomisation of bromine Hοat[½Br2(l)] +111.9 kJ mol–1

Enthalpy change of atomisation of copper, Hοat[Cu(s)] +338.3 kJ mol–1
First ionisation energy of copper, Em1[Cu(g)] +746.0 kJ mol–1
Second ionisation energy of copper, Em2 [Cu(g)] +1958.0 kJ mol–1
Electron affinity of bromine, Eaff[Br(g)] –342.6 kJ mol–1
Enthalpy change of formation of CuBr2(s), Hοf [CuBr2(s)] –141.8 kJ mol–1

(a) On the following outline of a Born-Haber cycle complete the boxes A, B, and C by
putting in the formula and state symbol for the appropriate species and writing the
name of the enthalpy change D.
C u 2 + (g ) + 2 B r – (g ) C u B r 2 (s)

C D ...........................................

C u (s) + B r 2 (l)

(3)

http://www.epingsoft.com
Generated by Direct DocX to Doc

(b) Use the data to calculate a value for the lattice energy of copper(II) bromide.

Give a sign and units in your answer.

(3)

(c) When the lattice energy of copper(II) bromide is calculated from ionic radii and
charges, the result is a value numerically about 10% less than the one obtained from
the Born-Haber cycle.

(i) What does this suggest about the nature of the bonding in copper(II) bromide?

...........................................................................................................................

...........................................................................................................................
(1)

(ii) Draw a diagram to show how the smaller copper ion alters the shape of the larger
bromide ion.

(1)
(Total 8 marks)

http://www.epingsoft.com

Chemistry Enthalpy Calculations
0% (1)
Chemistry Enthalpy Calculations
121 pages
CHM1 Energetics
No ratings yet
CHM1 Energetics
179 pages
Energetics I 2 QP
No ratings yet
Energetics I 2 QP
13 pages
CHM1 Energetics Q
No ratings yet
CHM1 Energetics Q
90 pages
Applications of He Sss Law
No ratings yet
Applications of He Sss Law
91 pages
(Pearson) IB Chemistry HL
No ratings yet
(Pearson) IB Chemistry HL
5 pages
5.2 (152 Marks) : 1. (1 Mark)
No ratings yet
5.2 (152 Marks) : 1. (1 Mark)
42 pages
Methanol Combustion & Entropy Analysis
No ratings yet
Methanol Combustion & Entropy Analysis
231 pages
Thermochemistry 12.11.24
No ratings yet
Thermochemistry 12.11.24
75 pages
Application of Hess's Law 5 QP
No ratings yet
Application of Hess's Law 5 QP
7 pages
Topic 2 - Thermochemistry
No ratings yet
Topic 2 - Thermochemistry
4 pages
Energetics - CAPE Chemistry Unit 1
No ratings yet
Energetics - CAPE Chemistry Unit 1
38 pages
THERMOCHEMISTRY
No ratings yet
THERMOCHEMISTRY
11 pages
Energetics Y12
No ratings yet
Energetics Y12
17 pages
Energetics Questions
100% (1)
Energetics Questions
58 pages
5 3+back
No ratings yet
5 3+back
6 pages
Chemistry Enthalpy Worksheet
No ratings yet
Chemistry Enthalpy Worksheet
11 pages
Chemical Energetics
No ratings yet
Chemical Energetics
29 pages
Sem 2 Test1 FC
No ratings yet
Sem 2 Test1 FC
18 pages
Enthalpy Change & Hess’s Law Guide
No ratings yet
Enthalpy Change & Hess’s Law Guide
77 pages
Lattice Enthalpy Entropy Free Energy
No ratings yet
Lattice Enthalpy Entropy Free Energy
53 pages
Chemistry Exam: Hess's Law Applications
No ratings yet
Chemistry Exam: Hess's Law Applications
103 pages
Applicationsof Hessslaw
No ratings yet
Applicationsof Hessslaw
92 pages
Thermodynamics 7
No ratings yet
Thermodynamics 7
15 pages
8 Calculating Enthalpy Change Standard Enthalpy of Formation
No ratings yet
8 Calculating Enthalpy Change Standard Enthalpy of Formation
6 pages
2011 Enthalpy Tutorial (With Ans)
100% (1)
2011 Enthalpy Tutorial (With Ans)
11 pages
Energetics Quiz
No ratings yet
Energetics Quiz
10 pages
Mod 3 Hard Q Edit
No ratings yet
Mod 3 Hard Q Edit
13 pages
Energy and Energy Changes
No ratings yet
Energy and Energy Changes
24 pages
Topic 7 Chemical Energetics - n9 Questions
No ratings yet
Topic 7 Chemical Energetics - n9 Questions
11 pages
Energetics Questions
No ratings yet
Energetics Questions
263 pages
Keilan Crawford - Y12 Paper 1 Exam Pack - Physical Chemistry
No ratings yet
Keilan Crawford - Y12 Paper 1 Exam Pack - Physical Chemistry
19 pages
Answer Scheme Practice CORONA - 1-1
100% (1)
Answer Scheme Practice CORONA - 1-1
12 pages
Thermodynamics 4
No ratings yet
Thermodynamics 4
11 pages
Thermo p2 SL 2019: Markscheme
No ratings yet
Thermo p2 SL 2019: Markscheme
7 pages
Thermodynamics Worksheet
No ratings yet
Thermodynamics Worksheet
2 pages
Enthalpy Review Questions
100% (1)
Enthalpy Review Questions
3 pages
Thermochemistry Hess - S Law
No ratings yet
Thermochemistry Hess - S Law
8 pages
t2 Chem Revision Ex 6 - Answer Scheme
No ratings yet
t2 Chem Revision Ex 6 - Answer Scheme
9 pages
Thermochemistry PDF
No ratings yet
Thermochemistry PDF
74 pages
Thermochemistry Assignment
No ratings yet
Thermochemistry Assignment
12 pages
Thermochemistry for Chemistry Students
100% (3)
Thermochemistry for Chemistry Students
34 pages
4 Thermochemistry
100% (1)
4 Thermochemistry
34 pages
Bond Enthalpies 4 QP
No ratings yet
Bond Enthalpies 4 QP
9 pages
Hess's Law and Enthalpy Calculations
No ratings yet
Hess's Law and Enthalpy Calculations
6 pages
Energetics Practice H2 Chemistry
100% (1)
Energetics Practice H2 Chemistry
2 pages
Application of Hesss Law 4 QP
No ratings yet
Application of Hesss Law 4 QP
8 pages
AS Level Chemistry Energetics Test
No ratings yet
AS Level Chemistry Energetics Test
10 pages
Entalpy of Formation
100% (1)
Entalpy of Formation
28 pages
Energetics Question Bank
No ratings yet
Energetics Question Bank
18 pages
2.0 Thermochemistry Dec 21
No ratings yet
2.0 Thermochemistry Dec 21
77 pages
Energetics Test
No ratings yet
Energetics Test
10 pages
Chemistry Enthalpy Exercises
No ratings yet
Chemistry Enthalpy Exercises
13 pages
Workheet 5.15.2
No ratings yet
Workheet 5.15.2
4 pages
Calorimetry Problems - Solutions
100% (1)
Calorimetry Problems - Solutions
3 pages
Name - Honors Chemistry - / - / - Hess's Law
No ratings yet
Name - Honors Chemistry - / - / - Hess's Law
4 pages
Energetics Worksheet Revision 1 - Hess - S Cycle - Calorimetry
No ratings yet
Energetics Worksheet Revision 1 - Hess - S Cycle - Calorimetry
3 pages
Thermochemistry Worksheet
No ratings yet
Thermochemistry Worksheet
5 pages
Ammonia Synthesis Reactors
No ratings yet
Ammonia Synthesis Reactors
4 pages
Lesson 4 Thermochemistry
No ratings yet
Lesson 4 Thermochemistry
8 pages
Topic 2 - Thermochemistry
No ratings yet
Topic 2 - Thermochemistry
25 pages
Chemical Thermodynamics: Module - 4
No ratings yet
Chemical Thermodynamics: Module - 4
25 pages
Amount of Substance A-Level Only
No ratings yet
Amount of Substance A-Level Only
154 pages
Thermochemistry Class Notes-290 PDF
No ratings yet
Thermochemistry Class Notes-290 PDF
19 pages
C-Nitroso Compounds: Synthesis & Bioactivity
No ratings yet
C-Nitroso Compounds: Synthesis & Bioactivity
21 pages
Bond Dissociation Energies Table
100% (1)
Bond Dissociation Energies Table
34 pages
S3.1 HL
No ratings yet
S3.1 HL
54 pages
NCHE 312 Assignment 2
No ratings yet
NCHE 312 Assignment 2
15 pages
Thermo Dynamics
100% (1)
Thermo Dynamics
22 pages
CHE1010 Tutorial Sheet 6
No ratings yet
CHE1010 Tutorial Sheet 6
4 pages
Born Haber Cycle
No ratings yet
Born Haber Cycle
6 pages
Chemical Thermodynamics Guide
No ratings yet
Chemical Thermodynamics Guide
36 pages
Chem 626: Spring 2013
No ratings yet
Chem 626: Spring 2013
5 pages
OCR 2023 Chemistry AS Level Paper
No ratings yet
OCR 2023 Chemistry AS Level Paper
24 pages
AQA AS Chemistry 4 Practice Question Answers
No ratings yet
AQA AS Chemistry 4 Practice Question Answers
3 pages
CHM 4155 Polymer Chemistry Textbook
No ratings yet
CHM 4155 Polymer Chemistry Textbook
291 pages
4.7 Exam Question Practice
No ratings yet
4.7 Exam Question Practice
3 pages
Thermal Decomposition of 1 Pentanol and Its Isomers: A Theoretical Study
No ratings yet
Thermal Decomposition of 1 Pentanol and Its Isomers: A Theoretical Study
7 pages
Chemical Bonding Notes-1
No ratings yet
Chemical Bonding Notes-1
5 pages
Chemistry Exam Questions
No ratings yet
Chemistry Exam Questions
27 pages
Thermodynamics: DPPs
No ratings yet
Thermodynamics: DPPs
25 pages
Cbte33 e
No ratings yet
Cbte33 e
45 pages
Jaipur Region
No ratings yet
Jaipur Region
8 pages
Basic Concepts: 1.1 Bond Dissociation Energy
100% (1)
Basic Concepts: 1.1 Bond Dissociation Energy
31 pages
Bondenthalpies
No ratings yet
Bondenthalpies
66 pages
Gr. 12 Thermochemistry Cheat Sheet
No ratings yet
Gr. 12 Thermochemistry Cheat Sheet
4 pages