plumiAverage bond enthalpies: OCR A‑Level Chemistry A questions
OCR A-Level Chemistry A past-paper questions on 3.2.1.4 Average bond enthalpies, 2016–2025, with mark schemes and examiner’s reports where available.
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All 22 questions on Average bond enthalpies, as a list
- June 2025, Paper 1, Q6 (1 mark): Methane reacts with oxygen as shown in the equation: CO2(g) + 2H2O(g) ΔrH = –730 kJ mol–1 CH4(g) + 2O2(g) The table shows some bond enthalpies. Bond O–H O=O C=O
- June 2025, AS Paper 1, Q23(b) (3 marks): The displayed formulae of SO2 and SO3 are shown below. O S O O S O O The bond enthalpies for the S=O bond in SO2 and SO3 are not the same. The table shows bond
- June 2024, Paper 3, Q2(a)(i) (1 mark): Why do all average bond enthalpies have a positive value? [1]
- June 2024, Paper 3, Q2(a)(ii) (3 marks): Determine the C–H bond enthalpy, in kJ mol–1, using the information above. C–H bond enthalpy = kJ mol–1 [3]
- June 2024, AS Paper 1, Q23(b) (3 marks): Hydrazine, N2H4, shown below, can be used as a rocket fuel. H H N N H H As a fuel, N2H4 reacts with oxygen as shown below. N2(g) + 2H2O(g) ΔH = –581 kJ mol–1 N2
- June 2023, AS Paper 2, Q4(c)(i) (4 marks): Use this value of ΔcH and the average bond enthalpies below to calculate the average bond enthalpy of C=O. Average bond enthalpy / Bond kJ mol–1 C–H +413 C–C +3
- June 2023, AS Paper 2, Q4(c)(ii) (2 marks): Methoxymethane, CH3OCH3, is an isomer of ethanol. On combustion, methoxymethane, in the gaseous state, produces carbon dioxide and steam. H H H C O C H(g) + 3 O
- June 2022, Paper 1, Q7 (1 mark): Bond enthalpies are shown in the table. Bond C–C C–H O–H C–O C=O O–O O=O Bond enthalpy 347 435 464 358 805 144 498 / kJ mol–1 What is the enthalpy change, in kJ
- June 2022, AS Paper 2, Q4(b) (3 marks): Hydrogen can also be manufactured by reacting ethanol with steam, as shown in Equilibrium 4.2. H H H C C O H + 3 H O H 6 H H + 2 O C O Equilibrium 4.2 H H Avera
- November 2021, Paper 1, Q8 (1 mark): Bond enthalpies are given in the table. Bond H–S O=O S=O O–H Bond enthalpy +346 +498 +531 +464 / kJ mol–1 What is the enthalpy change, in kJ mol–1, for the reac
- November 2021, AS Paper 1, Q22(c) (3 marks): The reaction for the production of hydrogen is repeated below. 3H2(g) + CO(g) ∆H = +206 kJ mol–1 CH4(g) + H2O(g) Average bond enthalpies are shown in the table.
- November 2020, Paper 3, Q3(b) (6 marks): Propane, C3H8, (boiling point −42 °C) is used as ‘camping gas’. A student plans to determine the enthalpy change of combustion of propane, ∆cH (C3H8), by two me
- November 2020, AS Paper 1, Q11 (1 mark): Hydrogen and oxygen react as shown below. 2H2(g) + O2(g) → 2H2O(g) ∆rH = −486 kJ mol−1 Bond enthalpies are shown in the table. Bond H−H O=O Bond enthalpy +436 +
- June 2019, Paper 1, Q19(a)(i) (1 mark): Explain why the enthalpy change for Reaction 1 has a negative value. Use ideas about enthalpy changes associated with bond breaking and bond making. [1]
- June 2018, Paper 1, Q13 (1 mark): Which enthalpy change(s) is/are endothermic? 1 The bond enthalpy of the C–H bond 2 The second electron affinity of oxygen 3 The standard enthalpy change of form
- June 2018, Paper 1, Q16(b)(i) (2 marks): Explain what is meant by the term average bond enthalpy. [2]
- June 2018, Paper 1, Q16(b)(ii) (3 marks): Calculate the bond enthalpy of the F–F bond. bond enthalpy = kJ mol–1 [3]
- June 2018, AS Paper 2, Q3(c) (2 marks): Hydrogen reacts with chlorine to form hydrogen chloride, HCl: 2HCl(g) ∆H = –184 kJ mol–1 H2(g) + Cl2(g) Table 3.1 shows bond enthalpies. Bond Enthalpy/kJ mol–1
- June 2017, Paper 1, Q9 (1 mark): Enthalpy values are provided below. 2HI(g) ΔrH = –9 kJ mol–1 H2(g) + I2(g) Bond enthalpy Bond / kJ mol–1 H–H +436 I – I +151 What is the bond enthalpy, in kJ mo
- June 2017, AS Paper 1, Q25(a)(i) (1 mark): Explain, in terms of bond breaking and bond forming, why a reaction can be exothermic. [1]
- June 2017, AS Paper 1, Q25(a)(ii) (3 marks): Average bond enthalpies are shown in the table. Average bond enthalpy Bond /kJ mol–1 O–H +464 O=O +498 C–H +413 C=O +805 Calculate the average bond enthalpy of
- June 2016, AS Paper 2, Q4(a)(i) (1 mark): Explain, in terms of bond breaking and bond making, why the enthalpy change of formation of NO is endothermic. [1]
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