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1 This question is about fuels and energy production.
3
The diagram shows the apparatus used to compare the energy released when 100 cm of water
is heated by burning different liquid fuels, J, K, L and M.
thermometer
clamp
100 cm3 water copper can
liquid fuel
All conditions are kept the same apart from the type of fuel and mass of fuel burned.
The results are shown.
mass of fuel burned increase in temperature
fuel
/g / °C
J 2 4
K 4 8
L 1 3
M 2 5
Deduce which fuel, J, K, L or M, releases the most energy per gram.
.................................................................................................................................................. [1]
[Total: 1]
2 Name the type of chemical reaction that releases heat energy.
.................................................................................................................................................. [1]
[Total: 1]
2
3 An energy level diagram for the burning of a fuel is shown.
energy
progress of reaction
Complete the diagram using these words:
• products
• reactants. [1]
[Total: 1]
4 Chemical reactions can be endothermic or exothermic.
State the meaning of the term endothermic.
..................................................................................................................................................
.................................................................................................................................................. [1]
[Total: 1]
5 Ethane is an alkane which undergoes a photochemical reaction with chlorine as shown.
C2H6(g) + Cl2(g) → C2H5Cl(l) + HCl(g)
The energy profile diagram of this reaction is shown.
A
C2H6 + Cl 2
energy
B
C2H5Cl + HCl
progress of reaction
(a) Name the energy change labelled A.
........................................................................................................................................... [1]
3
(b) Name the energy change labelled B.
........................................................................................................................................... [1]
(c) State how the energy profile diagram shows this is an exothermic reaction.
........................................................................................................................................... [1]
[Total: 3]
6 The chemical equation for a reaction can be represented as shown.
H H H H
C C + Br Br ® Br C C Br
H H H H
Some bond energies are given.
bond energy
bond
in kJ/mol
C−H 410
C=C 610
Br−Br 190
C−C 350
C−Br 290
Use the bond energies in the table to calculate the energy change in this reaction.
Use the following steps.
(a) Calculate the energy needed to break bonds.
energy = ..................................... kJ [1]
4
(b) Calculate the energy released in making bonds.
energy = .................................... kJ [1]
(c) Determine the energy change in this reaction.
energy change in this reaction = .....................kJ/mol [1]
[Total: 3]
7 When nitric acid reacts with calcium hydroxide, the temperature of the reaction mixture increases.
(a) Choose the word which best describes this reaction.
Draw a circle around your chosen answer.
decomposition endothermic exothermic oxidation
[1]
(b) Complete the energy level diagram for the reaction of nitric acid with calcium hydroxide by
writing the words:
• reactants
• products.
energy
progress of reaction
[1]
[Total: 2]
8 Bromine monochloride, BrCl, is made by the reaction between bromine and chlorine.
5
The chemical equation is shown.
Br2(g) + Cl2(g) → 2BrCl(g)
bond energy in
bond
kJ / mol
Br-Br 190
Cl-Cl 242
Br-Cl 218
Calculate the overall energy change for the reaction using bond energies.
Use the following steps.
(a) Calculate the total amount of energy required to break the bonds in 1 mole of Br2(g) and
1 mole of Cl2(g).
.................................................. k J [1]
(b) Calculate the total amount of energy released when the bonds in 2 moles of BrCl(g) are formed.
....................................................kJ [1]
(c) Calculate the overall energy change for the reaction.
............................................kJ / mol [1]
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[Total: 3]
9 Fuel cells are used to generate electricity.
(a) Name the reactants in a fuel cell.
........................................................................................................................................... [1]
(b) Name the waste product of a fuel cell.
........................................................................................................................................... [1]
[Total: 2]
10 This question is about chemical reactions and electricity.
The diagram shows the apparatus used in the production of electrical energy in a simple cell.
voltmeter
V
zinc electrode iron electrode
electrolyte
The reading on the voltmeter can be increased if either zinc or iron is replaced by another metal.
(a) Name a metal that can replace zinc and increase the reading on the voltmeter.
........................................................................................................................................... [1]
(b) Name a metal that can replace iron and increase the reading on the voltmeter.
........................................................................................................................................... [1]
[Total: 2]
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11 The chemical equation for a reaction can be represented as shown.
H H H H
C C + Cl Cl Cl C C Cl
H H H H
The energy change for the reaction is −180 kJ / mol.
Use the bond energies in the table to calculate the bond energy of a C−Cl bond, in kJ / mol.
bond C−H C=C Cl−Cl C−C
bond energy in kJ / mol 410 610 240 350
Use the following steps.
step 1 Calculate the energy needed to break bonds.
energy needed to break bonds = ..................................... kJ
step 2 Use your answer in step 1 and the energy change for the reaction to determine the energy
released when bonds are formed.
energy released when bonds form = ............................... kJ
step 3 Use your answer in step 2 and bond energy values to determine the energy of a C−Cl bond.
bond energy of a C−Cl bond = .................................kJ / mol [4]
[Total: 4]
12 Chlorine reacts with carbon monoxide to produce phosgene gas, COCl2(g). A catalyst is used.
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Cl2(g) + CO(g) ⇌ COCl2(g)
The reaction is exothermic.
(a) Explain why the reaction is exothermic in terms of the energy changes of bond breaking and
bond making.
...........................................................................................................................................
...........................................................................................................................................
........................................................................................................................................... [3]
(b) (i) Complete the energy level diagram for this reaction.
On your diagram show:
• the product of the reaction
• an arrow representing the energy change, labelled ΔH
• an arrow representing the activation energy, labelled ΔA. [3]
Cl 2(g) + CO(g)
energy
progress of reaction
[3]
(ii) State why a catalyst is used.
................................................................................................................................ [1]
[Total: 7]
13 The isotope is radioactive
State the major use of this isotope of uranium.
.................................................................................................................................................. [1]
[Total: 1]
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14 State one use of hydrogen.
.................................................................................................................................................. [1]
[Total: 1]
15 This question is about the reactions of magnesium with nitric acid.
(a) The equation for the reaction of magnesium with concentrated nitric acid is shown.
Mg + 4HNO3 → Mg(NO3)2 + 2NO2 + 2H2O
(i) The reaction is exothermic
What is the meaning of the term exothermic?
................................................................................................................................ [1]
(ii) Which word best describes the compound Mg(NO3)2?
Draw a circle around the correct answer.
acid base oxide salt
[1]
[Total: 2]
16 When ammonium chloride dissolves in water, the temperature of the solution decreases.
What is the name for a reaction where the temperature of the solution decreases?
.................................................................................................................................................. [1]
[Total: 1]
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17 The reaction between ethanoic acid and ethanol is exothermic.
Draw an energy level diagram for this reaction.
On your diagram label:
● the reactants and products
● the energy change of the reaction, ΔH.
energy
progress of reaction
[3]
[Total: 3]
18 Solid hydrated copper(II) sulfate decomposes to anhydrous copper(II) sulfate when it is continuously
heated.
Is this an endothermic or an exothermic reaction?
Explain your answer.
..................................................................................................................................................
.................................................................................................................................................. [1]
[Total: 1]
11
19 Ethene is an alkene which reacts with bromine as shown in the equation.
C2H4 + Br2 → C2H4Br2
Part of the energy profile diagram of this reaction is shown.
C2H4 + Br2
energy
progress of reaction
The reaction is exothermic.
Complete the energy profile diagram for this reaction.
Include:
• the position of the products
• an arrow to show the activation energy, labelled as A
• an arrow to show the energy change for the reaction. [3]
[Total: 3]
20 Ammonia, NH3, is used to produce nitric acid, HNO3. This happens in a three-stage process.
Stage 1 is a redox reaction.
4NH3 + 5O2 → 4NO + 6H2O
(a) Identify what is oxidised in stage 1.
Give a reason for your answer.
substance oxidised ...........................................................................................................
reason ..............................................................................................................................
........................................................................................................................................... [2]
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(b) In this reaction the predicted yield of NO is 512 g. The actual yield is 384 g.
Calculate the percentage yield of NO in this reaction.
percentage yield of NO = ................................... [1]
(c) The equation for the reaction in stage 2 is shown.
2NO + O2 → 2NO2
Which major environmental problem does NO2 cause if it is released into the atmosphere?
...........................................................................................................................................
........................................................................................................................................... [1]
(d) The equation for the reaction in stage 3 is shown.
4NO2 + 2H2O + O2 → 4HNO3
Calculate the volume of O2 gas, at room temperature and pressure (r.t.p.), needed to produce
1260 g of HNO3.
Use the following steps.
• Calculate the number of moles of HNO3.
moles of HNO3 = ....................................
• Deduce the number of moles of O2 that reacted.
moles of O2 = .........................................
• Calculate the volume of O2 gas that reacts at room temperature and pressure (r.t.p.).
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volume of O2 gas = ...................................... dm [4]
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(e) The reaction in stage 3 is exothermic.
4NO2 + 2H2O + O2 → 4HNO3
Complete the energy level diagram for this reaction. Include an arrow that clearly shows the
energy change during the reaction.
4NO2 + 2H2O + O2
energy
progress of reaction
[3]
[Total: 11]
