IBDP Official Exam Material
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Topic 5: Energetics/Thermochemistry
For both SL and HL students
1. [1 mark]
What is the value for enthalpy of formation of methane from the given enthalpies of combustion?
C (s) + O2 (g) → CO2 (g) ΔH = −394 kJ mol−1
H2 (g) + 12O2 (g) → H2O (l) ΔH = −286 kJ mol−1
CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (l) ΔH = −891 kJ mol−1
A. (−394 − 286 − 891) kJ mol−1
B. (−394 − (2 × 286) − 891) kJ mol−1
C. (−394 − 286 + 891) kJ mol−1
D. (−394 − (2 × 286) + 891) kJ mol−1
2. [1 mark]
Which statement best describes heat?
A. A quantity of potential energy of particles
B. A quantity of average kinetic energy of particles
C. A quantity of energy transferred between particles
D. A quantity of the total energy held by particles
3. [1 mark]
The energy from burning 0.250 g of ethanol causes the temperature of 150 cm3 of water to rise by 10.5 °C. What is the enthalpy of combustion of ethanol, in kJ mol–1?
Specific heat capacity of water: 4.18 J g–1 K–1.
4. [1 mark]
What is the enthalpy change of the following reaction?
CH2CHCH2CH3 + HBr → CH3CHBrCH2CH3
A. –119.6 kJ
B. +119.6 kJ
C. –119.8 kJ
D. +119.8 kJ
5. [1 mark]
What is the correct interpretation of the following potential energy profile?
A. Endothermic reaction; products more stable than reactants.
B. Exothermic reaction; products more stable than reactants.
C. Endothermic reaction; products less stable than reactants.
D. Exothermic reaction; products less stable than reactants.
6. [1 mark]
What is correct about energy changes during bond breaking and bond formation?
7. [1 mark]
Which combination of ΔH1, ΔH2, and ΔH3 would give the enthalpy of the reaction?
CS2 (l) + 3O2 (g) → CO2 (g) + 2SO2 (g)
ΔH1 C (s) + O2 (g) → CO2 (g)
ΔH2 S (s) + O2 (g) → SO2 (g)
ΔH3 C (s) + 2S (s) → CS2 (l)
ΔH2 S (s) + O2 (g) → SO2 (g)
ΔH3 C (s) + 2S (s) → CS2 (l)
A. ΔH = ΔH1 + ΔH2 + ΔH3
B. ΔH = ΔH1 + ΔH2 − ΔH3
C. ΔH = ΔH1 + 2(ΔH2) + ΔH3
D. ΔH = ΔH1 + 2(ΔH2) − ΔH3
8. [1 mark]
Which statement is correct about identical pieces of magnesium added to two solutions, X and Y, containing hydrochloric acid at the same temperature?
A. Solution X will reach a higher maximum temperature.
B. Solution Y will reach a higher maximum temperature.
C. Solutions X and Y will have the same temperature rise.
D. It is not possible to predict whether X or Y will have the higher maximum temperature because we cannot identify the limiting reactant.
9. [1 mark]
Cold packs contain ammonium nitrate and water separated by a membrane.
The mass of the contents of the cold pack is 25.32 g and its initial temperature is 25.2 °C. Once the contents are mixed, the temperature drops to 0.8 °C.
Calculate the energy, in J, absorbed by the dissolution of ammonium nitrate in water within the cold pack. Assume the specific heat capacity of the solution is 4.18 J g−1 K−1. Use section 1 of the data booklet.
10a. [1 mark]
Cold packs contain ammonium nitrate and water separated by a membrane.
The mass of the contents of the cold pack is 25.32 g and its initial temperature is 25.2 °C. Once the contents are mixed, the temperature drops to 0.8 °C.
Calculate the energy, in J, absorbed by the dissolution of ammonium nitrate in water within the cold pack. Assume the specific heat capacity of the solution is 4.18 J g−1 K−1. Use section 1 of the data booklet.
10b. [2 marks]
The change in enthalpy when ammonium nitrate dissolves in water is 25.69 kJ mol−1. Determine the mass of ammonium nitrate in the cold pack using your answer obtained in (10)(a) and section 6 of the data booklet.
If you did not obtain an answer in (e)(i), use 3.11 × 103 J, although this is not the correct answer.
10c. [3 marks]
The absolute uncertainty in mass of the contents of the cold pack is ±0.01 g and in each temperature reading is ±0.2 °C. Using your answer in (10)(b), calculate the absolute uncertainty in the mass of ammonium nitrate in the cold pack.
If you did not obtain an answer in (10)(b), use 6.55 g, although this is not the correct answer.
11. [3 marks]
Chlorine reacts with methane.
CH4 (g) + Cl2 (g) → CH3Cl (g) + HCl (g)
Calculate the enthalpy change of the reaction, ΔH, using section 11 of the data booklet.
12. [2 marks]
Draw and label an enthalpy level diagram for this reaction.
13. [1 mark]
Which combustion reaction releases the least energy per mole of C3H8?
Approximate bond enthalpy / kJ mol−1
O=O 500
C=O 800
C≡O 1000
O=O 500
C=O 800
C≡O 1000
A. C3H8 (g) + 5O2 (g) → 3CO2 (g) + 4H2O (g)
B. C3H8 (g) + 92O2 (g) → 2CO2 (g) + CO (g) + 4H2O (g)
C. C3H8 (g) + 4O2 (g) → CO2 (g) + 2CO (g) + 4H2O (g)
D. C3H8 (g) + 72O2 (g) → 3CO (g) + 4H2O (g)
14. [1 mark]
Which equation represents the standard enthalpy of formation of lithium oxide?
A. 4Li (s) + O2 (g) → 2Li2O (s)
B. 2Li (s) + 12O2 (g) → Li2O (s)
C. Li (s) + 14O2 (g) → 12Li2O (s)
D. Li (g) + 14O2 (g) → 12Li2O (g)
15. [1 mark]
Which statement describes an endothermic reaction?
A. The bonds broken are stronger than the bonds formed.
B. The enthalpy of the reactants is higher than the enthalpy of the products.
C. The temperature of the surroundings increases.
D. The products are more stable than the reactants.
16. [1 mark]
Which is the enthalpy change of reaction, ΔH?
17. [1 mark]
What is the heat change, in kJ, when 100.0 g of aluminium is heated from 19.0 °C to 32.0 °C?
Specific heat capacity of aluminium: 0.90 J g−1 K−1
A. 0.90×100.0×13.0
B. 0.90×100.0×286
C. 0.90×100.0×13.0/1000
D. 0.90×100.0×286/1000
18. [3 marks]
Consider the first stage of the reaction.
CH4 (g) + H2O (g) ⇌ CO (g) + 3H2 (g)
Determine the enthalpy change, ΔH, in kJ. Use section 11 of the data booklet.
Bond enthalpy of CO = 1077 kJ mol−1.
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