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Energetics: OCR A‑Level Chemistry B questions

Every OCR A-Level Chemistry B exam question on DF Energetics (specification points DF(d)–(g)), 2016–2025, with its mark scheme and examiner’s report.

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2,049 questions

  1. Q23(c)(i)

    June 2025 · AS Paper 1

    1 markDF Energetics
    The whole paper ↗
    June 2025 AS Paper 1, question 23(c)(i): Which one-word term describes a reaction with a negative enthalpy change? [1]

  2. Q23(c)(ii)

    June 2025 · AS Paper 1

    1 markDF Energetics
    The whole paper ↗
    June 2025 AS Paper 1, question 23(c)(ii): Explain, in terms of bonds broken and made, why some enthalpy changes are negative. [1] Question 3(c) starts on Page 16

  3. Q23(d)(i)

    June 2025 · AS Paper 1

    3 marksDF Energetics
    The whole paper ↗
    June 2025 AS Paper 1, question 23(d)(i): The students obtain the following results. Mass of burner + C6H12 at start 20.2 g Mass of burner + C6H12 at end 17.6 g Mass of water in beaker 505 g Temperature

  4. Q23(d)(ii)

    June 2025 · AS Paper 1

    3 marksDF Energetics
    The whole paper ↗
    June 2025 AS Paper 1, question 23(d)(ii): The value in (i) is less negative than the Data Book value. A student makes two statements: • One reason for this is that some C6H12 vapour might have evaporate

  5. Q4(b)

    June 2024 · Paper 3

    1 markDF Energetics
    The whole paper ↗
    June 2024 Paper 3, question 4(b): What term describes a reaction where the temperature decreases? [1]

  6. Q5

    June 2024 · AS Paper 1

    1 markDF Energetics
    The whole paper ↗
    June 2024 AS Paper 1, question 5: This question is about the relationship between enthalpy changes and bonds broken and made. Which row is correct? sign of ΔH description bonds broken and made m

  7. Q21(c)(i)

    June 2024 · AS Paper 1

    3 marksDF Energetics
    The whole paper ↗
    June 2024 AS Paper 1, question 21(c)(i): (Assume there are 27.0 g of solution with the same specific heat capacity as water.) ΔH1 = kJ mol–1 [3]

  8. Q21(c)(ii)

    June 2024 · AS Paper 1

    1 markDF Energetics
    The whole paper ↗
    June 2024 AS Paper 1, question 21(c)(ii): The greatest measurement uncertainty is 0.05 g in the mass. What percentage is 0.05 of 2.0? answer = % [1]

  9. Q21(c)(iii)

    June 2024 · AS Paper 1

    2 marksDF Energetics
    The whole paper ↗
    June 2024 AS Paper 1, question 21(c)(iii): As well as measurement uncertainties, there are also errors caused by experimental limitations. One such error is ‘heat loss’ during the measurement of ΔH1. The

  10. Q21(c)(iv)

    June 2024 · AS Paper 1

    2 marksDF Energetics
    The whole paper ↗
    June 2024 AS Paper 1, question 21(c)(iv): The students do another experiment and calculate that ΔH2 = +22 kJ mol–1. Calculate ΔH in kJ mol–1, using your answer from (i) and the cycle in Fig. 21.1. ΔH =

  11. Q32(c)(i)

    June 2023 · Paper 1

    3 marksDF Energetics
    The whole paper ↗
    June 2023 Paper 1, question 32(c)(i): Use the results in Table 32.1 to calculate a value for the enthalpy change of combustion, ΔcH, of ethanol, C2H5OH, in kJ mol–1. ΔcH of ethanol = kJ mol–1 [3]

  12. Q32(c)(ii)

    June 2023 · Paper 1

    4 marksDF Energetics
    The whole paper ↗
    June 2023 Paper 1, question 32(c)(ii): The student found that the value of ΔcH obtained using this method was considerably less exothermic than that in a data book. State two sources of error in the

  13. Q32(d)(i)

    June 2023 · Paper 1

    1 markDF Energetics
    The whole paper ↗
    June 2023 Paper 1, question 32(d)(i): Why are the bond enthalpies in Table 32.2 described as average values? [1]

  14. Q32(d)(ii)

    June 2023 · Paper 1

    2 marksDF Energetics
    The whole paper ↗
    June 2023 Paper 1, question 32(d)(ii): The larger bond enthalpy of C=O compared with C–O implies that the C=O bond is shorter. Explain why double bonds are shorter than single bonds between the same

  15. Q32(d)(iii)

    June 2023 · Paper 1

    3 marksDF Energetics
    The whole paper ↗
    June 2023 Paper 1, question 32(d)(iii): The equation for the combustion of ethanol is shown below: 2CO2 + 3H2O ΔcH = –1367 kJ mol–1 Equation 32.1 C2H5OH + 3O2 Use the data in Table 32.2 and the value

  16. Q23(a)

    June 2023 · AS Paper 1

    1 markDF Energetics
    The whole paper ↗
    June 2023 AS Paper 1, question 23(a): The bond enthalpy for C–C in Table 23.1 is described as an average bond enthalpy. Explain the meaning of average in this context. [1]

  17. Q23(b)

    June 2023 · AS Paper 1

    3 marksDF Energetics
    The whole paper ↗
    June 2023 AS Paper 1, question 23(b): Use Equation 23.1 and data from Table 23.1 to calculate the bond enthalpy of C≡N in cyanogen. bond enthalpy = kJ mol–1 [3]

  18. Q23(c)(i)

    June 2023 · AS Paper 1

    2 marksDF Energetics
    The whole paper ↗
    June 2023 AS Paper 1, question 23(c)(i): Explain why the bond enthalpies in Table 23.1 are all endothermic. [2]

  19. Q23(c)(ii)

    June 2023 · AS Paper 1

    1 markDF Energetics
    The whole paper ↗
    June 2023 AS Paper 1, question 23(c)(ii): Use the information in Table 23.1 to compare the relative bond lengths in CO and CO2. [1]

  20. Q23(d)(i)

    June 2023 · AS Paper 1

    3 marksDF Formulae, equations and amount of substanceDF Energetics
    The whole paper ↗
    June 2023 AS Paper 1, question 23(d)(i): Complete labelled diagrams of simple apparatus that could be used for Experiment 1 and Experiment 2. Experiment 1 Experiment 2 flow of cyanogen flow of cyanogen
All 73 questions on Energetics, as a list
  1. June 2025, AS Paper 1, Q23(c)(i) (1 mark): Which one-word term describes a reaction with a negative enthalpy change? [1]
  2. June 2025, AS Paper 1, Q23(c)(ii) (1 mark): Explain, in terms of bonds broken and made, why some enthalpy changes are negative. [1] Question 3(c) starts on Page 16
  3. June 2025, AS Paper 1, Q23(d)(i) (3 marks): The students obtain the following results. Mass of burner + C6H12 at start 20.2 g Mass of burner + C6H12 at end 17.6 g Mass of water in beaker 505 g Temperature
  4. June 2025, AS Paper 1, Q23(d)(ii) (3 marks): The value in (i) is less negative than the Data Book value. A student makes two statements: • One reason for this is that some C6H12 vapour might have evaporate
  5. June 2024, Paper 3, Q4(b) (1 mark): What term describes a reaction where the temperature decreases? [1]
  6. June 2024, AS Paper 1, Q5 (1 mark): This question is about the relationship between enthalpy changes and bonds broken and made. Which row is correct? sign of ΔH description bonds broken and made m
  7. June 2024, AS Paper 1, Q21(c)(i) (3 marks): (Assume there are 27.0 g of solution with the same specific heat capacity as water.) ΔH1 = kJ mol–1 [3]
  8. June 2024, AS Paper 1, Q21(c)(ii) (1 mark): The greatest measurement uncertainty is 0.05 g in the mass. What percentage is 0.05 of 2.0? answer = % [1]
  9. June 2024, AS Paper 1, Q21(c)(iii) (2 marks): As well as measurement uncertainties, there are also errors caused by experimental limitations. One such error is ‘heat loss’ during the measurement of ΔH1. The
  10. June 2024, AS Paper 1, Q21(c)(iv) (2 marks): The students do another experiment and calculate that ΔH2 = +22 kJ mol–1. Calculate ΔH in kJ mol–1, using your answer from (i) and the cycle in Fig. 21.1. ΔH =
  11. June 2023, Paper 1, Q32(c)(i) (3 marks): Use the results in Table 32.1 to calculate a value for the enthalpy change of combustion, ΔcH, of ethanol, C2H5OH, in kJ mol–1. ΔcH of ethanol = kJ mol–1 [3]
  12. June 2023, Paper 1, Q32(c)(ii) (4 marks): The student found that the value of ΔcH obtained using this method was considerably less exothermic than that in a data book. State two sources of error in the
  13. June 2023, Paper 1, Q32(d)(i) (1 mark): Why are the bond enthalpies in Table 32.2 described as average values? [1]
  14. June 2023, Paper 1, Q32(d)(ii) (2 marks): The larger bond enthalpy of C=O compared with C–O implies that the C=O bond is shorter. Explain why double bonds are shorter than single bonds between the same
  15. June 2023, Paper 1, Q32(d)(iii) (3 marks): The equation for the combustion of ethanol is shown below: 2CO2 + 3H2O ΔcH = –1367 kJ mol–1 Equation 32.1 C2H5OH + 3O2 Use the data in Table 32.2 and the value
  16. June 2023, AS Paper 1, Q23(a) (1 mark): The bond enthalpy for C–C in Table 23.1 is described as an average bond enthalpy. Explain the meaning of average in this context. [1]
  17. June 2023, AS Paper 1, Q23(b) (3 marks): Use Equation 23.1 and data from Table 23.1 to calculate the bond enthalpy of C≡N in cyanogen. bond enthalpy = kJ mol–1 [3]
  18. June 2023, AS Paper 1, Q23(c)(i) (2 marks): Explain why the bond enthalpies in Table 23.1 are all endothermic. [2]
  19. June 2023, AS Paper 1, Q23(c)(ii) (1 mark): Use the information in Table 23.1 to compare the relative bond lengths in CO and CO2. [1]
  20. June 2023, AS Paper 1, Q23(d)(i) (3 marks): Complete labelled diagrams of simple apparatus that could be used for Experiment 1 and Experiment 2. Experiment 1 Experiment 2 flow of cyanogen flow of cyanogen
  21. June 2023, AS Paper 1, Q23(d)(ii) (1 mark): Describe one improvement that could have been made to Experiment 2 to improve the accuracy of the result. [1]
  22. June 2023, AS Paper 1, Q23(d)(iii) (4 marks): Calculate the maximum possible temperature rise of the water. Use the scientists’ result and measurements from part (d) and Equation 23.1. Give your answer to a
  23. June 2022, Paper 3, Q2(a)(ii) (3 marks): The student measures the temperature of the contents of the beaker over a period of 20 minutes and plots the data on the graph below. 32 31 30 highest temp 29 2
  24. June 2022, Paper 3, Q2(b) (1 mark): Calculate ΔrH o for Reaction 2.1 using the data shown below. ΔfH o / kJ mol–1 Cu2+(aq) + 64.4 Zn2+(aq) –152.4 ΔrH o = kJ mol–1 [1]
  25. June 2022, Paper 3, Q2(c) (6 marks): This question is about the enthalpy change of the reaction of zinc with copper(II) sulfate solution. (c)* The value obtained from the student’s experiment is co
  26. June 2022, AS Paper 1, Q20 (1 mark): What represents the enthalpy change of neutralisation of sulfuric acid? A H2SO4 + 2NaOH Na2SO4 + 2H2O 1 1 B 2H2SO4 + NaOH 2Na2SO4 + H2O C H2SO4 + 2Na Na2SO4 + H
  27. June 2022, AS Paper 2, Q4(c)(i) (3 marks): Methanol burns in oxygen as shown in equation 4.1. CO2(g) + 2H2O(g) ΔcH298 = –676 kJ mol–1 CH3OH(g) + 1½O2(g) Equation 4.1 Some average bond enthalpy data are g
  28. June 2022, AS Paper 2, Q4(c)(ii) (1 mark): The standard enthalpy change of combustion of methanol (ΔcH o 298) is not the same as the value given in equation 4.1. Give a reason for this. [1]
  29. June 2022, AS Paper 2, Q4(d) (3 marks): A student carries out an experiment to measure ΔcH for methanol, CH3OH. The student burns the methanol in a spirit burner below a beaker containing 100 cm3 wate
  30. June 2022, AS Paper 2, Q4(e) (6 marks): Vehicles using petrol as fuel will still be on the roads for some time to come. It is important that developments continue to improve fuel efficiency and furthe
  31. November 2021, Paper 1, Q4 (1 mark): Which equation represents the enthalpy change of formation of CO2? A C(s) + 2O(g) CO2(g) B C(s) + O2(g) CO2(g) C CO(g) + 0.5O2(g) CO2(g) D C(g) + O2(g) CO2(g) Y
  32. November 2021, AS Paper 1, Q6 (1 mark): Which statement is correct for an endothermic reaction? A Heat is given out. B More bonds are made than broken. C More energy is taken in to break bonds than is
  33. November 2021, AS Paper 1, Q24(b)(i) (2 marks): Complete a labelled diagram of their apparatus. spirit burner containing butan-1-ol [2]
  34. November 2021, AS Paper 1, Q24(b)(ii) (3 marks): The students find that the combustion of 2.5 g of butan-1-ol raises the temperature of 200 cm3 of water by 52 °C. Calculate their value for ∆cH for butan-1-ol,
  35. November 2021, AS Paper 1, Q24(c)(i) (2 marks): Use the data below to complete a Hess cycle and calculate ∆cH o for butan-1-ol, C4H9OH(l). ∆fHo/ kJ mol–1 Substance C4H9OH(l) –327 CO2(g) –394 H2O(l) –286 C4H9O
  36. November 2021, AS Paper 1, Q24(c)(ii) (1 mark): Suggest one reason why the answers to parts (b)(ii) and (c)(i) are not the same. [1]
  37. November 2020, Paper 3, Q3(a) (3 marks): A student measures the enthalpy change of combustion of propan-1-ol, C3H7OH. The apparatus used is shown in Fig. 3.1. thermometer clamp metal can water spirit b
  38. November 2020, Paper 3, Q3(b)(i) (2 marks): One reason for the difference is heat loss to the surroundings. Suggest two other reasons for the difference between the experimental value and the data book va
  39. November 2020, Paper 3, Q3(b)(ii) (1 mark): Describe one addition to the apparatus in Fig. 3.1 that would improve the accuracy of the experimental value for the enthalpy change of combustion. [1]
  40. November 2020, Paper 3, Q3(c)(ii) (3 marks): Explain why the enthalpy change of combustion values are exothermic and very similar. Use your answer to (c)(i) and the idea of average bond enthalpies in your
  41. November 2020, AS Paper 2, Q4(a) (1 mark): Suggest why it is difficult to measure ΔH1 directly. [1]
  42. November 2020, AS Paper 2, Q4(b) (2 marks): A student does an experiment to measure ΔH2. The student adds 7.50 × 10–2 mol of NaHCO3 to 50.00 cm3 (an excess) of 2.00 mol dm−3 HCl. The temperature decreases
  43. November 2020, AS Paper 2, Q4(c) (6 marks): Sodium hydrogencarbonate is used in baking powder. When it is heated above about 80 °C it begins to break down as shown in equation 4.1. 2NaHCO3(s) Na2CO3(s) +
  44. November 2020, AS Paper 2, Q4(d) (4 marks): In separate accurately performed experiments the following enthalpy changes were determined. ΔH2 = +23 kJ mol−1 NaHCO3(s) + HCl (aq) NaCl (aq) + CO2(g) + H2O(l)
  45. November 2020, AS Paper 2, Q4(e) (2 marks): Bond enthalpies can be used in some calculations involving ΔH values. Use the data below to calculate a value for the bond enthalpy of the H–O bond. 2H2O(g) ΔH
  46. November 2020, AS Paper 2, Q4(f) (1 mark): Why can bond enthalpies not be used to estimate ΔH1? 2NaHCO3(s) Na2CO3(s) + CO2(g) + H2O(l) ΔH1 [1]
  47. June 2019, Paper 1, Q34(c) (3 marks): Another theory is that life developed near hot vents deep under the sea. At these hot vents geothermally heated water rich in minerals emerges from the ocean fl
  48. June 2019, Paper 2, Q5(a) (3 marks): The enthalpy change of combustion of acetylene, C2H2, can be calculated using enthalpy changes of formation. Draw the Hess cycle that shows this, giving formula
  49. June 2019, AS Paper 1, Q21(a) (1 mark): Write down the value of ∆fH o for NH3(g). Include the unit in your answer. [1]
  50. June 2019, AS Paper 1, Q23(a)(i) (3 marks): Calculate the enthalpy change on dissolving 1 mol of ammonium nitrate in water. Give your answer in kJ mol–1 and to an appropriate number of significant figures
  51. June 2019, AS Paper 1, Q23(a)(ii) (2 marks): The students want to get a larger temperature change. Some suggest using a greater mass of ammonium nitrate, others suggest using more water. Evaluate the stude
  52. June 2019, AS Paper 1, Q23(b)(i) (5 marks): The students are provided with powdered zinc metal and solid CuSO4•5H2O (Mr = 250). They measure the temperature rise when 100 cm3 (an excess) of 0.2 mol dm–3 c
  53. June 2019, AS Paper 1, Q23(b)(ii) (2 marks): The students repeat the experiment, measuring the temperature at different times. They plot the graph shown. 28 26 24 22 temperature / °C 20 18 16 14 12 0 2 4 6
  54. June 2018, Paper 1, Q31(b)(i) (1 mark): Describe an experiment they could use to determine the enthalpy change of combustion of liquid hexane in the laboratory. [1]
  55. June 2018, Paper 1, Q31(b)(ii) (1 mark): Show how the result would be calculated from the measurements made when carrying out the experiment in part (b)(i). [1]
  56. June 2018, Paper 1, Q31(b)(iii) (2 marks): Describe two ways in which the students could make the basic experiment more accurate. 1 2 [2]
  57. June 2018, Paper 1, Q31(c) (2 marks): The students are given some enthalpy changes of formation and use them to check the accuracy of their answer. Calculate the standard enthalpy change of combusti
  58. June 2018, AS Paper 2, Q2(b) (2 marks): Explain why the combustion of butan-1-ol is exothermic, using ideas about bond-breaking and bond-making. You do not need to list the specific bonds broken and m
  59. June 2018, AS Paper 2, Q2(d) (3 marks): In a simple laboratory experiment, the combustion of 1.00 g of a biofuel compound raised the temperature of 500 g of water by 16.0 °C. Calculate a value for the
  60. June 2018, AS Paper 2, Q2(e) (1 mark): The laboratory set-up used to obtain the data in part (d) is shown below. thermometer/stirrer 500 g water in glass beaker flame from burning biofuel This set-up
  61. June 2018, AS Paper 2, Q2(f) (3 marks): Another alcohol that is used in some fuels is methanol, CH3OH. An equation for the complete combustion of methanol is shown below. CO2(g) + 2H2O(g) ΔcH = –677 k
  62. June 2017, Paper 1, Q14 (1 mark): Why are many bond enthalpies described as averages? A They are averaged out over many molecules with different kinetic energies. B They are averaged out over di
  63. June 2017, AS Paper 1, Q16 (1 mark): What is correct about an exothermic reaction? A Heat is taken in. B More bonds are made than broken. C The sign of ∆H is positive. D It is represented by a down
  64. June 2017, AS Paper 1, Q23(b)(i) (2 marks): Calculate a value for the ∆fH of fuel C using the data below. C7H16(l) + 11O2(g) 7CO2(g) + 8H2O(l) ∆cH = –4811kJ mol–1 fuel C ∆fH / kJ mol–1 Compound CO2(g) –39
  65. June 2017, AS Paper 1, Q23(c)(i) (2 marks): State the measurements that the students would make to calculate a value for the energy produced. Show how these measurements would be used to calculate this en
  66. June 2017, AS Paper 1, Q23(c)(ii) (4 marks): State and explain two improvements that could be made to increase the accuracy of the calculated value of the energy produced. 1 2 [4]
  67. June 2016, AS Paper 2, Q1(a) (2 marks): Write a chemical equation to represent the standard enthalpy change of combustion of butane (ΔcH ○). Show state symbols. [2]
  68. June 2016, AS Paper 2, Q1(b) (3 marks): Calculate a value for the enthalpy change of combustion (in kJ mol–1) of butane (ΔcH) using the experimental results in Table 1.1. enthalpy change of combustion
  69. June 2016, AS Paper 2, Q1(c)(i) (1 mark): Estimate the standard enthalpy change of combustion of butane. ΔcH ○ = kJ mol–1 [1]
  70. June 2016, AS Paper 2, Q1(c)(ii) (2 marks): Suggest two reasons, apart from ‘heat losses’, why the value calculated in the simple experiment in (b) is much less exothermic than the value estimated. 1 2 [2
  71. June 2016, AS Paper 2, Q1(c)(iii) (1 mark): The students repeat the experiment using the same thermometer and balance. State and explain one way in which they could modify the procedure in order to obtain
  72. June 2016, AS Paper 2, Q1(d) (1 mark): The enthalpy change of combustion of butane can be measured directly using the method in (b). The standard enthalpy change of formation of butane is represented
  73. June 2016, AS Paper 2, Q1(f) (3 marks): The enthalpy change of combustion of methanol and some bond enthalpies are shown below. CH3OH(g) + 11 CO2(g) + 2H2O(g) ΔcH = –726 kJ mol–1 2O2(g) Bond enthalpy

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