1. What energy changes occur when chemical bonds are formed and broken?
A. Energy is absorbed when bonds are formed and when they are broken.
B. Energy is released when bonds are formed and when they are broken.
C. Energy is absorbed when bonds are formed and released when they are broken.
D. Energy is released when bonds are formed and absorbed when they are broken.
(Total 1 mark)
2. The temperature of a 2.0 g sample of aluminium increases from 25°C to 30°C.
–1 –1
How many joules of heat energy were added? (Specific heat of Al = 0.90 J g K )
A. 0.36
B. 2.3
C. 9.0
D. 11
(Total 1 mark)
3. Using the equations below:
C(s) + O2(g) → CO2(g) ∆H = –390 kJ
Mn(s) + O2(g) → MnO2(s) ∆H = –520 kJ
what is ∆H (in kJ) for the following reaction?
MnO2(s) + C(s) Mn(s) + CO2(g)
A. 910
B. 130
C. –130
D. –910
(Total 1 mark)
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4. Under what circumstances is a reaction spontaneous at all temperatures?
ο ο
∆H ∆S
A. + +
B. + –
C. – –
D. – +
(Total 1 mark)
5.
N um ber of
m o le c u le s
E a E n e rg y
The diagram shows the distribution of energy for the molecules in a sample of gas at a given
temperature, T1.
(a) In the diagram Ea represents the activation energy for a reaction. Define this term.
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(1)
2
(b) On the diagram above draw another curve to show the energy distribution for the same
gas at a higher temperature. Label the curve T 2.
(2)
(c) With reference to your diagram, state and explain what happens to the rate of a reaction
when the temperature is increased.
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(2)
(Total 5 marks)
6. Which combination of ionic charge and ionic radius give the largest lattice enthalpy for an ionic
compound?
Ionic charge Ionic radius
A. high large
B. high small
C. low small
D. low large
(Total 1 mark)
7. What is ∆H for the reaction below in kJ?
CS2(g) + 3O2(g) CO2(g) + 2SO2(g)
–1
[∆Hf /kJ mol : CS2(g) 110, CO2(g) – 390, SO2(g) – 290]
A. –570
B. –790
C. –860
D. –1080
(Total 1 mark)
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8. Which statements about exothermic reactions are correct?
I. They have negative H values.
II. The products have a lower enthalpy than the reactants.
III. The products are more energetically stable than the reactants.
A. I and II only
B. I and III only
C. II and III only
D. I, II and III
(Total 1 mark)
9. A sample of a metal is heated. Which of the following are needed to calculate the heat absorbed
by the sample?
I. The mass of the sample
II. The density of the sample
III. The specific heat capacity of the sample
A. I and II only
B. I and III only
C. II and III only
D. I, II and III
(Total 1 mark)
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–1
10. The average bond enthalpies for O—O and O==O are 146 and 496 kJ mol respectively.
What is the enthalpy change, in kJ, for the reaction below?
H—O—O—H(g) H—O—H(g) + ½O==O(g)
A. – 102
B. + 102
C. + 350
D. + 394
(Total 1 mark)
11. Which reaction has the greatest positive entropy change?
A. CH4(g) + 1½O2(g) → CO(g) + 2H2O(g)
B. CH4(g) + 1½O2(g) → CO(g) + 2H2O(l)
C. CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)
D. CH4(g) + 2O2(g) → CO2(g) + 2H2O(l)
(Total 1 mark)
12. Given the following data:
–1
C(s) + F2(g) → CF4(g); ∆H1 = –680 kJ mol
–1
F2(g) → 2F(g); ∆H2 = +158 kJ mol
–1
C(s) → C(g); ∆H3 = +715 kJ mol
5
–1
calculate the average bond enthalpy (in kJ mol ) for the C––F bond.
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(Total 4 marks)
13. For the process:
C6H6(l) C6H6(s)
the standard entropy and enthalpy changes are:
ο –1 ο –1 –1
∆H = –9.83kJ mol and ∆S = –35.2J K mol .
Predict and explain the effect of an increase in temperature on the spontaneity of the process.
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(Total 3 marks)
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14. What is the energy change (in kJ) when the temperature of 20 g of water increases by 10°C?
A. 20×10×4.18
B. 20×283×4.18
20 10 4.18
C. 1000
20 283 4.18
D. 1000
(Total 1 mark)
15. The lattice enthalpy values for lithium fluoride and calcium fluoride are shown below.
ο –1
LiF(s) ∆H = +1022 kJ mol
ο –1
CaF2(s) ∆H = +2602 kJ mol
Which of the following statements help(s) to explain why the value for lithium fluoride is less
than that for calcium fluoride?
I. The ionic radius of lithium is less than that of calcium.
II. The ionic charge of lithium is less than that of calcium.
A. I only
B. II only
C. I and II
D. Neither I nor II
(Total 1 mark)
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16. When the solids Ba(OH)2 and NH4SCN are mixed, a solution is produced and the
temperature drops.
Ba(OH)2(s) + 2NH4SCN(s) → Ba(SCN)2(aq) + 2NH3(g) + 2H2O(l)
Which statement about the energetics of this reaction is correct?
A. The reaction is endothermic and H is negative.
B. The reaction is endothermic and H is positive.
C. The reaction is exothermic and H is negative.
D. The reaction is exothermic and H is positive.
(Total 1 mark)
17. Using the equations below
1
ο
Cu(s) + 2 O2(g) → CuO(s)∆H = –156 kJ
1
ο
2Cu(s) + 2 O2(g) → Cu2O(s)∆H = –170 kJ
ο
what is the value of ∆H (in kJ) for the following reaction?
1
2CuO(s) → Cu2O(s) + 2 O2(g)
A. 142
B. 15
C. –15
D. –142
(Total 1 mark)
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18. Which reaction occurs with the largest increase in entropy?
A. Pb(NO3)2(s) + 2KI(s) → PbI2(s) + 2KNO3(s)
B. CaCO3(s) → CaO(s) + CO2(g)
C. 3H2(g) + N2(g) → 2NH3(g)
D. H2(g) + I2(g) → 2HI(g)
(Total 1 mark)
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19. The ∆H and ∆S values for a certain reaction are both positive. Which statement is correct
about the spontaneity of this reaction at different temperatures?
A. It will be spontaneous at all temperatures.
B. It will be spontaneous at high temperatures but not at low temperatures.
C. It will be spontaneous at low temperatures but not at high temperatures.
D. It will not be spontaneous at any temperature.
(Total 1 mark)
20. Which of the quantities in the enthalpy level diagram below is (are) affected by the use of a
catalyst?
I II
E n th a lp y
III
Time
9
A. I only
B. III only
C. I and II only
D. II and III only
(Total 1 mark)
ο ο ο
21. Explain in terms of G , why a reaction for which both H andS values are positive can
sometimes be spontaneous and sometimes not.
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(Total 4 marks)
22. Consider the following reaction.
N2(g) +3H2(g) → 2NH3(g)
ο
(i) Use values from Table 10 in the Data Booklet to calculate the enthalpy change, H , for
this reaction.
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(3)
10
–1 –1
(ii) The magnitude of the entropy change, S, at 27°C for the reaction is 62.7 J K mol .
State, with a reason, the sign of S.
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(2)
(iii) Calculate G for the reaction at 27°C and determine whether this reaction is spontaneous
at this temperature.
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(3)
(Total 8 marks)
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