plumiHess’s law and enthalpy cycles (Core Practical 2): Edexcel International A Level Chemistry questions
Edexcel International A Level Chemistry past-paper questions on 6.1.4 Hess’s law and enthalpy cycles (Core Practical 2), 2019–2025, with mark schemes and examiner’s reports where available.
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All 38 questions on Hess’s law and enthalpy cycles (Core Practical 2), as a list
- June 2025, AS Unit 2, Q2(b) (1 mark): A data book value for the standard enthalpy change of combustion of methane is –890 kJ mol–1. What is the experimental value for the enthalpy change of vaporisa
- June 2025, AS Unit 2, Q17(b)(i) (3 marks): Calculate ΔrH1 for Reaction 1. Include a sign and units in your answer. [Assume the specific heat capacity of the solution = 4.18 J g–1 °C–1 the density of the
- June 2025, AS Unit 2, Q17(b)(ii) (3 marks): The enthalpy change of decomposition, ΔrH , of magnesium carbonate can be found using a Hess cycle. Calculate the enthalpy change of decomposition by using a co
- June 2025, AS Unit 2, Q17(b)(iii) (1 mark): Give a reason why it is not possible to measure the enthalpy change for the decomposition directly. (1)
- June 2025, Unit 4, Q19(a)(i) (2 marks): Using the data in the table, calculate the standard enthalpy change, ΔrHd, for this reaction. (2)
- June 2025, Unit 5, Q16(a)(i) (1 mark): Complete the cycle by adding balancing numbers. (1) C(g) + H(g) C6H6(g) C(s) + H2(g) C6H6(l)
- October 2024, AS Unit 2, Q16(b)(ii) (2 marks): In the second experiment, the student determined the enthalpy change when dissolving hydrated magnesium sulfate. MgSO4·7H2O(s) + (aq) → MgSO4(aq) ∆H = +15.8 kJ
- October 2024, AS Unit 2, Q16(b)(iii) (2 marks): Calculate the enthalpy change when anhydrous magnesium sulfate forms hydrated magnesium sulfate, using the completed Hess cycle and your answer in (b)(i). (2)
- June 2024 (R), AS Unit 2, Q18(b)(i) (2 marks): Complete the Hess cycle with two arrows and correct species and state symbols in the box. (2) ΔrH MgCO3(s) MgO(s) + CO2(g)
- June 2024 (R), AS Unit 2, Q18(b)(ii) (2 marks): Calculate the enthalpy change for the thermal decomposition of magnesium carbonate, ∆rH . Include a sign and units in your answer. (2)
- January 2024, AS Unit 2, Q22(c) (2 marks): Calculate the enthalpy change of reaction, ΔrH1 , for Reaction 1. Use your answer to (b), the data provided and the enthalpy cycle shown. [If you did not calcul
- October 2023, AS Unit 2, Q2 (1 mark): Which expression gives the standard enthalpy change, in kJ mol–1, for the reaction shown? BaCO3(s) → BaO(s) + CO2(g) ΔfH d values: BaCO3(s) = –1216 kJ mol–1 BaO
- October 2023, Unit 4, Q16(a)(ii) (3 marks): Calculate the standard enthalpy change for this reaction. . (3)
- June 2023, AS Unit 2, Q3 (1 mark): The enthalpy changes for two reactions are shown. 2Fe(s) + 1½O2(g) → Fe2O3(s) ΔrH = –824 kJ mol–1 + ½O2(g) → CO(g) ΔrH = –111 kJ mol–1 C(s) What is the enthalpy
- January 2023, AS Unit 2, Q22(g)(i) (2 marks): Complete the enthalpy cycle. (2) Enthalpy cycle ΔrH NH3(g) + HNO3(aq) NH4NO3(aq) –32.6 kJ mol–1 kJ mol–1 NH4NO3(s) –220.2 kJ mol–1 kJ mol–1 N2(g) + 2H2(g) + 1½O
- January 2023, AS Unit 2, Q22(g)(ii) (1 mark): Calculate the enthalpy change, ΔrH , in kJ mol–1 , for the reaction of NH3(g) with HNO3(aq). (1)
- January 2023, Unit 4, Q20(a)(ii) (2 marks): Calculate the enthalpy change of reaction, ΔrH d, for the cracking of butane. Include a sign and units with your answer. (2)
- October 2022, AS Unit 2, Q3 (1 mark): Some enthalpy changes of combustion are shown. Substance Enthalpy change of combustion / kJ mol−1 CH3CHO(l) −1167 C(s) −394 H2(g) −286 What is the enthalpy chan
- October 2022, AS Unit 2, Q20(b)(i) (2 marks): Complete the Hess cycle. (2) CuSO4(s) + 5H2O(l) CuSO4·5H2O(s)
- October 2022, AS Unit 2, Q20(b)(ii) (2 marks): Calculate the enthalpy change when anhydrous copper(II) sulfate forms hydrated copper(II) sulfate. Include a sign and units. (2)
- June 2022, Unit 4, Q21(a)(i) (2 marks): Calculate the standard enthalpy change, ∆rH , for the reduction of iron(III) oxide by carbon. (2)
- January 2022, AS Unit 2, Q21(b)(ii) (2 marks): Complete the Hess cycle. C4H10O(l) + O2(g) CO2(g) + H2O(l) 4C(s, graphite) + + (2)
- January 2022, AS Unit 2, Q21(b)(iii) (2 marks): Calculate the standard enthalpy change of combustion of 2‑methylpropan‑2‑ol using the data in the table and the completed Hess cycle. (2)
- October 2021, AS Unit 2, Q19(c) (3 marks): Enthalpy changes of combustion can be used to calculate the enthalpy change of formation of a compound. Standard enthalpy change of combustion, Substance ∆cH /
- October 2021, AS Unit 3, Q3(d)(i) (1 mark): Calculate the enthalpy change of hydration for the conversion of anhydrous copper(II) sulfate to hydrated copper(II) sulfate crystals. (1)
- October 2021, AS Unit 3, Q3(d)(ii) (1 mark): Give one possible reason why the enthalpy change of hydration in (d)(i) could not be found directly by experiment. (1)
- June 2021, AS Unit 2, Q22(b)(ii) (4 marks): The standard enthalpy change of formation for phosgene is ΔfH = –220.1 kJ mol–1. Complete the Hess cycle and determine the standard enthalpy change of formation
- January 2021, AS Unit 2, Q12 (1 mark): The enthalpy changes for two reactions are shown. H+(aq) + OH−(aq) → H2O(l) ΔrH = −57.2 kJ mol−1 CH3COOH(aq) + OH−(aq) → CH3COO−(aq) + H2O(l) ΔrH = −56.0 kJ mol
- January 2021, AS Unit 2, Q21(c) (5 marks): Ammonium ethanoate, CH3COONH4(s), is used to control the pH of foods. It can be formed by the reaction of pure ethanoic acid, CH3COOH(l), with ammonium carbonat
- January 2021, AS Unit 3, Q3(c)(ii) (1 mark): Using your answer to (c)(i), calculate the enthalpy change, ΔrH , for the thermal decomposition of this Group 2 carbonate in kJ mol−1. Include a sign with your
- October 2020, AS Unit 2, Q10(c) (1 mark): Hess’s Law can be applied to this system. Which expression is correct? (1) A v + x = u + w B w + x = u C u – w = v D u – v = x
- October 2020, AS Unit 2, Q13(a)(i) (1 mark): Add arrowheads and stoichiometric coefficients to the Hess’s Law diagram. (1) 3C(s) + 4H2(g) C3H8(g) CO2(g) + H2O(l)
- October 2020, AS Unit 2, Q13(a)(ii) (2 marks): Use the data at the start of the question and your Hess’s Law diagram to calculate the standard enthalpy change of formation of propane. Include a sign and unit
- January 2020, AS Unit 2, Q15(a)(iii) (1 mark): Complete the Hess cycle by adding two arrowheads. (1) ǻrH CuSO4(s) + 5H2O(l) CuSO4.5H2O(s) ǻsolnH(CuSO4) ǻsolnH(CuSO4.5H2O) CuSO4(aq)
- January 2020, AS Unit 2, Q15(a)(iv) (2 marks): Calculate the value for the enthalpy change ǻrH, in kJ mol−1, for the conversion of the anhydrous salt to the hydrated salt. Use the value from the table for ǻs
- January 2020, AS Unit 2, Q15(b) (2 marks): The hydration of anhydrous copper(II) sulfate is reversible. CuSO4(s) + 5H2O(l) CuSO4.5H2O(s) The forward reaction is exothermic. The temperature changes for bo
- June 2019, AS Unit 2, Q9 (1 mark): Use the data shown. ¨H = −858 kJ mol–1 CH4(g) + 2F2(g) → CF4(g) + 2H2(g) ¨H = −933 kJ mol–1 C(s) + 2F2(g) → CF4(g) What is the standard enthalpy change of forma
- June 2019, AS Unit 2, Q20(b)(ii) (2 marks): The Hess cycle and data to calculate the enthalpy change for the thermal decomposition of MgCO3 are shown. Mg(s) + C(s) + 1½O2(g) MgCO3(s) MgO(s) + CO2(g) 9 / k
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