plumiThermochemistry: WJEC A‑Level Chemistry questions
Every WJEC A-Level Chemistry exam question on 2.1 Thermochemistry, 2016–2025, with its mark scheme and examiner’s report.
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Calculations
Q9(a)
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Q6(a)
The whole paper ↗![Summer 2025 AS Unit 2, question 6(a): X + Y V + W [1] ΔHθ = kJ mol–1](https://pub-e8a9dbab8e2a4d089f52b2a45e0d0b50.r2.dev/bank/2410u20-jun25-06-a-qp.webp)
Q6(b)
The whole paper ↗![Summer 2025 AS Unit 2, question 6(b): V + W Z [1] ΔHθ = kJ mol–1](https://pub-e8a9dbab8e2a4d089f52b2a45e0d0b50.r2.dev/bank/2410u20-jun25-06-b-qp.webp)
Q8(b)(i)
The whole paper ↗![Summer 2025 AS Unit 2, question 8(b)(i): Give the meaning of the term standard enthalpy change of formation. [2]](https://pub-e8a9dbab8e2a4d089f52b2a45e0d0b50.r2.dev/bank/2410u20-jun25-08-bi-qp.webp)
Q8(b)(ii)
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Q8(c)(i)
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Q8(c)(ii)
The whole paper ↗![Summer 2025 AS Unit 2, question 8(c)(ii): Use the balanced equation to calculate the mass of water released during this reaction. Give your answer to an appropriate number of significant figures. [3] Ba](https://pub-e8a9dbab8e2a4d089f52b2a45e0d0b50.r2.dev/bank/2410u20-jun25-08-cii-qp.webp)
Q8(c)(iii)
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Q8(d)(i)
The whole paper ↗![Summer 2025 AS Unit 2, question 8(d)(i): Explain why the experimental value calculated in part (c)(iii) is much lower than the theoretical value calculated in part (b)(ii). [1]](https://pub-e8a9dbab8e2a4d089f52b2a45e0d0b50.r2.dev/bank/2410u20-jun25-08-di-qp.webp)
Q8(d)(ii)
The whole paper ↗![Summer 2025 AS Unit 2, question 8(d)(ii): Suggest a possible change to the method that would improve the accuracy of the experimentally determined value. [1]](https://pub-e8a9dbab8e2a4d089f52b2a45e0d0b50.r2.dev/bank/2410u20-jun25-08-dii-qp.webp)
Q8(d)(ii)
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Q9(a)(ii)
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Q12(a)
The whole paper ↗![Summer 2024 AS Unit 2, question 12(a): State what is meant by the enthalpy change of combustion. [2]](https://pub-e8a9dbab8e2a4d089f52b2a45e0d0b50.r2.dev/bank/2410u20-jun24-12-a-qp.webp)
Q12(b)(i)
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Q12(b)(ii)
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Q12(c)
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Q8(d)(i)
The whole paper ↗![Summer 2023 Unit 3, question 8(d)(i): Calculate the standard enthalpy change of formation of potassium dichromate, K2Cr2O7. [2] ∆fHθ = kJ mol−1](https://pub-e8a9dbab8e2a4d089f52b2a45e0d0b50.r2.dev/bank/1410u30-jun23-08-di-qp.webp)
Q10(a)(i)
The whole paper ↗![Summer 2023 AS Unit 2, question 10(a)(i): into the insulated cups. [1]](https://pub-e8a9dbab8e2a4d089f52b2a45e0d0b50.r2.dev/bank/2410u20-jun23-10-ai-qp.webp)
Q10(a)(ii)
The whole paper ↗![Summer 2023 AS Unit 2, question 10(a)(ii): State why a higher maximum temperature is recorded when increasing volumes of sodium hydroxide are added. [1]](https://pub-e8a9dbab8e2a4d089f52b2a45e0d0b50.r2.dev/bank/2410u20-jun23-10-aii-qp.webp)
All 66 questions on Thermochemistry, as a list
- Summer 2025, Unit 3, Q9(a) (3 marks): Use data from one of the tables below to calculate the more accurate value of the standard enthalpy change for reaction 1 Give a reason for your choice of data.
- Summer 2025, AS Unit 2, Q6(a) (1 mark): X + Y V + W [1] ΔHθ = kJ mol–1
- Summer 2025, AS Unit 2, Q6(b) (1 mark): V + W Z [1] ΔHθ = kJ mol–1
- Summer 2025, AS Unit 2, Q8(b)(i) (2 marks): Give the meaning of the term standard enthalpy change of formation. [2]
- Summer 2025, AS Unit 2, Q8(b)(ii) (3 marks): this reaction are given below. ΔfHθ / kJ mol–1 Substance H2O –286 NH3 –45.9 BaCl2.2H2O –1460 Ba(OH)2.8H2O –3350 NH4Cl –314 Using a Hess cycle or otherwise, calc
- Summer 2025, AS Unit 2, Q8(c)(i) (4 marks): A student performed an experiment to determine the enthalpy change for this reaction. He weighed 31.5 g of hydrated barium hydroxide into a glass beaker and rec
- Summer 2025, AS Unit 2, Q8(c)(ii) (3 marks): Use the balanced equation to calculate the mass of water released during this reaction. Give your answer to an appropriate number of significant figures. [3] Ba
- Summer 2025, AS Unit 2, Q8(c)(iii) (2 marks): Use the mass of water from part (ii) and the maximum temperature change from part (i) to calculate the enthalpy change of reaction per mole of hydrated barium h
- Summer 2025, AS Unit 2, Q8(d)(i) (1 mark): Explain why the experimental value calculated in part (c)(iii) is much lower than the theoretical value calculated in part (b)(ii). [1]
- Summer 2025, AS Unit 2, Q8(d)(ii) (1 mark): Suggest a possible change to the method that would improve the accuracy of the experimentally determined value. [1]
- Summer 2024, Unit 3, Q8(d)(ii) (9 marks): This catalyst is used to catalyse the oxidation of sulfur dioxide. ΔHθ = –197 kJ mol–1 2SO2(g) + O2(g) 2SO3(g) ΔSθ = –187 J K–1 mol–1 The standard enthalpy chan
- Summer 2024, Unit 3, Q9(a)(ii) (4 marks): Use the data below to calculate the standard enthalpy change of formation of AgBr(s) and hence show which of the two silver halides is more stable with respect
- Summer 2024, AS Unit 2, Q8 (6 marks): On heating, calcium hydroxide decomposes to produce calcium oxide and water. Ca(OH)2(s) CaO(s) + H2O(l) ΔH1 The enthalpy change of this reaction cannot be measu
- Summer 2024, AS Unit 2, Q12(a) (2 marks): State what is meant by the enthalpy change of combustion. [2]
- Summer 2024, AS Unit 2, Q12(b)(i) (4 marks): The equation that corresponds to the enthalpy change of combustion of propan-1-ol is shown. 1 C3H7OH(l) + 4 O2(g) 3CO2(g) + 4H2O(l) 2 The apparatus below can be
- Summer 2024, AS Unit 2, Q12(b)(ii) (1 mark): Another student suggested that leaving the spirit burner to burn for longer would increase the accuracy of the experiment. State whether you agree with this stu
- Summer 2024, AS Unit 2, Q12(c) (4 marks): Enthalpy changes of combustion can be used to determine average bond enthalpies. Some average bond enthalpies are given in the table. Bond Average bond enthalpy
- Summer 2023, Unit 3, Q8(d)(i) (2 marks): Calculate the standard enthalpy change of formation of potassium dichromate, K2Cr2O7. [2] ∆fHθ = kJ mol−1
- Summer 2023, AS Unit 2, Q10(a)(i) (1 mark): into the insulated cups. [1]
- Summer 2023, AS Unit 2, Q10(a)(ii) (1 mark): State why a higher maximum temperature is recorded when increasing volumes of sodium hydroxide are added. [1]
- Summer 2023, AS Unit 2, Q10(a)(iii) (2 marks): Explain why the maximum temperature recorded decreases when more than 30 cm3 of sodium hydroxide is added. [2]
- Summer 2023, AS Unit 2, Q10(a)(iv) (1 mark): On the graph, draw one straight line through the points that show an increase in maximum temperature and another straight line through the points that show a de
- Summer 2023, AS Unit 2, Q10(a)(v) (2 marks): From the graph, deduce the volume of sodium hydroxide needed to neutralise 25.0 cm3 of the methanoic acid solution and the temperature increase at that point. A
- Summer 2023, AS Unit 2, Q10(a)(vi) (2 marks): Use your answers to part (v) to calculate the amount of heat released by the neutralisation reaction. [2] Heat released = J
- Summer 2023, AS Unit 2, Q10(a)(vii) (3 marks): hence the enthalpy change of neutralisation of methanoic acid. [3] Enthalpy change of neutralisation = kJ mol–1
- Summer 2023, AS Unit 2, Q10(b) (2 marks): The experiment is repeated using hydrochloric acid instead of methanoic acid and a more negative value of the enthalpy change of neutralisation is calculated. S
- Summer 2022, AS Unit 2, Q5 (2 marks): State the meaning of the term ‘standard enthalpy change of formation’. [2] SECTION B Answer all questions.
- Summer 2022, AS Unit 2, Q7(b)(ii) (2 marks): The enthalpy change of combustion (ΔcHθ) for hexane is approximately –4160 kJ mol–1. Explain why the enthalpy change of combustion for the isomers of hexane sho
- Summer 2022, AS Unit 2, Q7(b)(iv) (6 marks): When hexane burns in a limited supply of oxygen it undergoes a different reaction known as incomplete combustion: C6H14 + 6.5O2 6CO + 7H2O The bond enthalpy val
- Summer 2022, AS Unit 2, Q10(a)(i) (2 marks): Plot the results on the graph paper below. [2] Time /s
- Summer 2022, AS Unit 2, Q10(a)(ii) (2 marks): Use your graph to calculate the maximum temperature change for this crystallisation. [2] maximum temperature change = °C
- Summer 2022, AS Unit 2, Q10(a)(iii) (4 marks): Use the total mass of the sodium ethanoate solution and the temperature change from the graph to calculate the enthalpy change of crystallisation per mole of so
- Summer 2022, AS Unit 2, Q10(a)(iv) (1 mark): Suggest a reason why the experimental enthalpy change is often lower than the theoretical enthalpy change. [1]
- Summer 2019, AS Unit 2, Q2 (2 marks): Write the equation that corresponds to the standard molar enthalpy change of formation of magnesium carbonate, MgCO3. [2]
- Summer 2019, AS Unit 2, Q7(a)(i) (3 marks): The equation for the reaction of calcium oxide with hydrochloric acid is shown. CaO(s) + 2HCl(aq) CaCl2(aq) + H2O(l) Use this equation to show that the hydrochl
- Summer 2019, AS Unit 2, Q7(a)(ii) (1 mark): Calculate the energy released in this reaction between calcium oxide and hydrochloric acid. [1] Energy released = J
- Summer 2019, AS Unit 2, Q7(a)(iii) (2 marks): Calculate the molar enthalpy change for the reaction between calcium oxide and hydrochloric acid. [2] CaO(s) + 2HCl(aq) CaCl2(aq) + H2O(l) Enthalpy change = kJ
- Summer 2019, AS Unit 2, Q7(a)(iv) (2 marks): The value of the molar enthalpy change of reaction for the reaction between calcium hydroxide and hydrochloric acid is –196 kJ mol–1. Use Hess’s Law and your an
- Summer 2019, AS Unit 2, Q7(a)(v) (2 marks): Suggest two changes to the apparatus shown that would give a more accurate value for the enthalpy changes of the reactions. Give a reason for your answer in bot
- Summer 2019, AS Unit 2, Q7(b)(i) (1 mark): Write the equation corresponding to the standard enthalpy change of combustion of methanol. [1]
- Summer 2019, AS Unit 2, Q7(b)(ii) (2 marks): Draw and label suitable apparatus as it is being used in an experiment to determine the enthalpy change of combustion of methanol. [2]
- Summer 2019, AS Unit 2, Q7(c)(i) (4 marks): Use this and the values of the average bond enthalpies in the table to calculate the average bond enthalpy of C—H. [4] Average bond enthalpy / kJ mol–1 Bond — C
- Summer 2019, AS Unit 2, Q7(c)(ii) (1 mark): State why the apparatus you have drawn in part (b) cannot be used to determine the enthalpy change of combustion of ethene. [1]
- Summer 2018, Unit 3, Q11(c) (2 marks): Use this information and the graph to calculate the standard enthalpy change of formation of hydrogen peroxide. [2] ΔfHθ(H2O2) = kJ mol–1
- Summer 2018, AS Unit 2, Q9(a)(i) (2 marks): The average bond enthalpy of a C Explain what is meant by bond enthalpy. [2]
- Summer 2018, AS Unit 2, Q9(a)(ii) (3 marks): Ethyne, C2H2, contains a C C. It reacts with hydrogen in a similar way to ethene. H C C H + 2H2 C2H6 Some average bond enthalpies are given in the table. Averag
- Summer 2018, AS Unit 2, Q9(b) (3 marks): Enthalpy changes of reaction are often found indirectly. The enthalpy change for the reaction of ethyne with hydrogen, as shown in part (a), can be determined b
- Summer 2018, AS Unit 2, Q9(c) (1 mark): The theoretical values that you have calculated in parts (a)(ii) and (b) are both the enthalpy change for the reaction between ethyne and hydrogen. Suggest a re
- Summer 2017, Unit 3, Q10(b) (1 mark): State why the enthalpy change of formation of Cl2(g) is zero. [1]
- Summer 2017, Unit 3, Q10(c) (2 marks): Calculate the standard enthalpy change of formation of HCl(g). [2] ΔfHθ = kJ mol−1
- Summer 2017, AS Unit 2, Q7(a) (2 marks): Ethanol, C2H5OH, is a liquid at room temperature. Write the equation that corresponds to the standard enthalpy change of formation of ethanol. [2]
- Summer 2017, AS Unit 2, Q7(b) (1 mark): Why is it difficult to measure the standard enthalpy change of formation of ethanol directly? [1]
- Summer 2017, AS Unit 2, Q7(c)(i) (3 marks): Explain how the enthalpy change of combustion is calculated from the results collected using this apparatus. [3]
- Summer 2017, AS Unit 2, Q7(c)(ii) (1 mark): Why is it difficult to use this apparatus to determine the enthalpy change of combustion of ethane, C2H6? [1]
- Summer 2017, AS Unit 2, Q7(d) (2 marks): Two students carried out an experiment using the apparatus in part (c). Neither followed the given method correctly. Euan extinguished the flame after only 10 s
- Summer 2017, AS Unit 2, Q7(e)(i) (3 marks): Use these data to calculate the standard enthalpy change of formation of ethanol. Show clearly how you carried out your calculation. [3] ΔfHθ = kJ mol–1
- Summer 2017, AS Unit 2, Q7(e)(ii) (2 marks): Amir said that hydrogen is the best fuel of these three in terms of the energy released by burning equal masses. Is he correct? Justify your answer. [2]
- Summer 2016, AS Unit 2, Q7(a) (3 marks): Draw a labelled diagram showing how the apparatus is set up to carry out this experiment. You should show how the heat losses could be minimised. [3]
- Summer 2016, AS Unit 2, Q7(b) (3 marks): Sian recorded the following data. Mass of magnesium strip = 0.1 g Initial temperature of acid = 21.0 °C Highest temperature reached = 35.5 °C Use these data to
- Summer 2016, AS Unit 2, Q7(c) (2 marks): hydrochloric acid. Although he used his data correctly to calculate the enthalpy change of reaction for 1 mol of magnesium, his answer was numerically much less
- Summer 2016, AS Unit 2, Q7(d) (2 marks): Sian used a one-decimal place balance to weigh the magnesium. Calculate the maximum percentage error in the mass of magnesium she used. Show clearly how you obt
- Summer 2016, AS Unit 2, Q7(e) (1 mark): Burning magnesium, when placed in a gas-jar containing chlorine, forms magnesium chloride and energy is released. Mg(s) + Cl2(g) MgCl2(s) Suggest why this react
- Summer 2016, AS Unit 2, Q8(a)(i) (2 marks): Define the term standard enthalpy change of combustion, ΔcH . [2]
- Summer 2016, AS Unit 2, Q8(a)(ii) (4 marks): The values of some average bond enthalpies are shown in the table below. Average bond enthalpy / kJ mol–1 Bond C C 348 O O 495 C O 799 O H 463 C2H6 + O2 2CO2 +
- Summer 2016, AS Unit 2, Q8(a)(iii) (1 mark): Suggest a reason why bond enthalpies are described as being average bond enthalpies. [1]
- Summer 2016, AS Unit 2, Q8(b) (6 marks): Charcoal consists mainly of carbon. It has been produced for many centuries by heating wood in the absence of oxygen. Natural gas consists mainly of methane and
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