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Chemical equilibrium: OCR A‑Level Chemistry A questions

Every OCR A-Level Chemistry A exam question on 3.2.3 Chemical equilibrium, 2016–2025, with its mark scheme and examiner’s report.

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1,820 questions

  1. Q3(a)

    June 2025 · Paper 3

    5 marks3.2.3 Chemical equilibrium5.1.2 How far?
    The whole paper ↗
    June 2025 Paper 3, question 3(a): Methanol, CH3OH, can be made industrially by the reaction of carbon monoxide, CO, with hydrogen, H2, in the presence of a catalyst. This is a reversible reactio

  2. Q12

    June 2025 · AS Paper 1

    1 mark3.2.2 Reaction rates3.2.3 Chemical equilibrium
    The whole paper ↗
    June 2025 AS Paper 1, question 12: Hydrogen and iodine react in the reaction below. H2(g) + I2(g) 2HI(g) Which row is correct when pressure is increased? Rate of reaction Equilibrium yield of HI

  3. Q23(a)

    June 2025 · AS Paper 1

    2 marks3.2.3 Chemical equilibrium
    The whole paper ↗
    June 2025 AS Paper 1, question 23(a): State two features of a dynamic equilibrium. 1 2 [2]

  4. Q23(c)

    June 2025 · AS Paper 1

    3 marks3.2.3 Chemical equilibrium
    The whole paper ↗
    June 2025 AS Paper 1, question 23(c): The table shows equilibrium concentrations for Equilibrium 23.1. [SO2(g)] / mol dm–3 [O2(g)] / mol dm–3 [SO3(g)] / mol dm–3 25.0 108 42.0 For Equilibrium 23.1 •

  5. Q11

    June 2024 · Paper 1

    1 mark3.2.3 Chemical equilibrium
    The whole paper ↗
    June 2024 Paper 1, question 11: The reversible reaction between hydrogen and iodine to form hydrogen iodide is H2(g) + I2(g) 2HI(g) The graph shows how the concentrations of the reactants and

  6. Q13

    June 2024 · AS Paper 1

    1 mark3.2.3 Chemical equilibrium
    The whole paper ↗
    June 2024 AS Paper 1, question 13: The reversible reaction below is at equilibrium. 2SO2(g) + O2(g) 2SO3(g) What is the expression for Kc? [SO2(g)]2 [O2(g)] A [SO3(g)]2 [SO3(g)]2 B [SO2(g)]2 [O2(

  7. Q23(a)(i)

    June 2024 · AS Paper 1

    2 marks3.2.3 Chemical equilibrium
    The whole paper ↗
    June 2024 AS Paper 1, question 23(a)(i): This is an example of a dynamic equilibrium. State 2 features of a dynamic equilibrium. 1 2 [2]

  8. Q23(a)(ii)

    June 2024 · AS Paper 1

    3 marks3.2.3 Chemical equilibrium
    The whole paper ↗
    June 2024 AS Paper 1, question 23(a)(ii): State and explain the conditions of temperature and pressure that would produce a large equilibrium yield of NH3. [3]

  9. Q15

    June 2023 · Paper 1

    1 mark3.2.3 Chemical equilibrium
    The whole paper ↗
    June 2023 Paper 1, question 15: Chlorine trifluoride can be decomposed into its elements forming the equilibrium mixture below. ∆H = +318 kJ mol–1 2Cl F3(g) Cl 2(g) + 3F2(g) colourless green y

  10. Q24(a)

    June 2023 · AS Paper 1

    1 mark3.2.3 Chemical equilibrium
    The whole paper ↗
    June 2023 AS Paper 1, question 24(a): Why is Equilibrium 24.1 a homogeneous equilibrium? [1]

  11. Q24(b)

    June 2023 · AS Paper 1

    5 marks3.2.3 Chemical equilibrium
    The whole paper ↗
    June 2023 AS Paper 1, question 24(b): Le Chatelier’s principle can be used to predict how different conditions affect the equilibrium position in Equilibrium 24.1. Explain how changing pressure, tem

  12. Q24(c)(i)

    June 2023 · AS Paper 1

    2 marks3.2.3 Chemical equilibrium
    The whole paper ↗
    June 2023 AS Paper 1, question 24(c)(i): Write the expression for Kc and calculate the numerical value for Kc in Equilibrium 24.1 at this constant temperature. Give your answer to an appropriate number

  13. Q24(c)(ii)

    June 2023 · AS Paper 1

    1 mark3.2.3 Chemical equilibrium
    The whole paper ↗
    June 2023 AS Paper 1, question 24(c)(ii): In the industrial production of SO3, an excess of O2(g) is used rather than a 2:1 proportion of SO2(g) to O2(g) which would match the stochiometry in Equilibriu

  14. Q4(a)

    June 2022 · Paper 3

    4 marks3.2.3 Chemical equilibrium3.2.2 Reaction rates
    The whole paper ↗
    June 2022 Paper 3, question 4(a): The students are supplied with the equilibrium mixture in Equilibrium 4.1 at room temperature. One student heats 20 cm3 of the mixture to 50 °C. • The other stu

  15. Q4(b)(ii)

    June 2022 · Paper 3

    3 marks3.2.3 Chemical equilibrium
    The whole paper ↗
    June 2022 Paper 3, question 4(b)(ii): Explain the changes in concentration of CoCl 4 Refer to Equilibrium 4.1 in your answer. [3]

  16. Q12

    June 2022 · AS Paper 1

    1 mark3.2.3 Chemical equilibrium
    The whole paper ↗
    June 2022 AS Paper 1, question 12: Which prediction can be made using le Chatelier’s principle? A The effect of a catalyst on the reaction rate. B The effect of a catalyst on the equilibrium posi

  17. Q13

    June 2022 · AS Paper 1

    1 mark3.2.3 Chemical equilibrium
    The whole paper ↗
    June 2022 AS Paper 1, question 13: Four equilibrium reactions are set up. The concentration of each gas in the equilibrium mixtures is 0.1 mol dm–3. Which equilibrium has a numerical Kc value of

  18. Q4(a)(i)

    June 2022 · AS Paper 2

    6 marks3.2.3 Chemical equilibrium
    The whole paper ↗
    June 2022 AS Paper 2, question 4(a)(i): In industry, hydrogen is manufactured from methane, as shown in Equilibrium 4.1. CO(g) + 3H2(g) ΔH = +206 kJ mol–1 CH4(g) + H2O(g) Equilibrium 4.1 The industria

  19. Q4(a)(ii)

    June 2022 · AS Paper 2

    2 marks3.2.3 Chemical equilibrium
    The whole paper ↗
    June 2022 AS Paper 2, question 4(a)(ii): A chemist mixes CH4(g) and H2O(g) and leaves the mixture to reach equilibrium. CO(g) + 3H2(g) ΔH = +206 kJ mol–1 CH4(g) + H2O(g) Equilibrium 4.1 The equilibrium

  20. Q9

    November 2021 · Paper 1

    1 mark3.2.3 Chemical equilibrium
    The whole paper ↗
    November 2021 Paper 1, question 9: An equilibrium system is shown below. CO(g) + NO2(g) CO2(g) + NO(g) Different amounts of CO, NO2, CO2 and NO are added to four containers, as shown below. Conta
All 47 questions on Chemical equilibrium, as a list
  1. June 2025, Paper 3, Q3(a) (5 marks): Methanol, CH3OH, can be made industrially by the reaction of carbon monoxide, CO, with hydrogen, H2, in the presence of a catalyst. This is a reversible reactio
  2. June 2025, AS Paper 1, Q12 (1 mark): Hydrogen and iodine react in the reaction below. H2(g) + I2(g) 2HI(g) Which row is correct when pressure is increased? Rate of reaction Equilibrium yield of HI
  3. June 2025, AS Paper 1, Q23(a) (2 marks): State two features of a dynamic equilibrium. 1 2 [2]
  4. June 2025, AS Paper 1, Q23(c) (3 marks): The table shows equilibrium concentrations for Equilibrium 23.1. [SO2(g)] / mol dm–3 [O2(g)] / mol dm–3 [SO3(g)] / mol dm–3 25.0 108 42.0 For Equilibrium 23.1 •
  5. June 2024, Paper 1, Q11 (1 mark): The reversible reaction between hydrogen and iodine to form hydrogen iodide is H2(g) + I2(g) 2HI(g) The graph shows how the concentrations of the reactants and
  6. June 2024, AS Paper 1, Q13 (1 mark): The reversible reaction below is at equilibrium. 2SO2(g) + O2(g) 2SO3(g) What is the expression for Kc? [SO2(g)]2 [O2(g)] A [SO3(g)]2 [SO3(g)]2 B [SO2(g)]2 [O2(
  7. June 2024, AS Paper 1, Q23(a)(i) (2 marks): This is an example of a dynamic equilibrium. State 2 features of a dynamic equilibrium. 1 2 [2]
  8. June 2024, AS Paper 1, Q23(a)(ii) (3 marks): State and explain the conditions of temperature and pressure that would produce a large equilibrium yield of NH3. [3]
  9. June 2023, Paper 1, Q15 (1 mark): Chlorine trifluoride can be decomposed into its elements forming the equilibrium mixture below. ∆H = +318 kJ mol–1 2Cl F3(g) Cl 2(g) + 3F2(g) colourless green y
  10. June 2023, AS Paper 1, Q24(a) (1 mark): Why is Equilibrium 24.1 a homogeneous equilibrium? [1]
  11. June 2023, AS Paper 1, Q24(b) (5 marks): Le Chatelier’s principle can be used to predict how different conditions affect the equilibrium position in Equilibrium 24.1. Explain how changing pressure, tem
  12. June 2023, AS Paper 1, Q24(c)(i) (2 marks): Write the expression for Kc and calculate the numerical value for Kc in Equilibrium 24.1 at this constant temperature. Give your answer to an appropriate number
  13. June 2023, AS Paper 1, Q24(c)(ii) (1 mark): In the industrial production of SO3, an excess of O2(g) is used rather than a 2:1 proportion of SO2(g) to O2(g) which would match the stochiometry in Equilibriu
  14. June 2022, Paper 3, Q4(a) (4 marks): The students are supplied with the equilibrium mixture in Equilibrium 4.1 at room temperature. One student heats 20 cm3 of the mixture to 50 °C. • The other stu
  15. June 2022, Paper 3, Q4(b)(ii) (3 marks): Explain the changes in concentration of CoCl 4 Refer to Equilibrium 4.1 in your answer. [3]
  16. June 2022, AS Paper 1, Q12 (1 mark): Which prediction can be made using le Chatelier’s principle? A The effect of a catalyst on the reaction rate. B The effect of a catalyst on the equilibrium posi
  17. June 2022, AS Paper 1, Q13 (1 mark): Four equilibrium reactions are set up. The concentration of each gas in the equilibrium mixtures is 0.1 mol dm–3. Which equilibrium has a numerical Kc value of
  18. June 2022, AS Paper 2, Q4(a)(i) (6 marks): In industry, hydrogen is manufactured from methane, as shown in Equilibrium 4.1. CO(g) + 3H2(g) ΔH = +206 kJ mol–1 CH4(g) + H2O(g) Equilibrium 4.1 The industria
  19. June 2022, AS Paper 2, Q4(a)(ii) (2 marks): A chemist mixes CH4(g) and H2O(g) and leaves the mixture to reach equilibrium. CO(g) + 3H2(g) ΔH = +206 kJ mol–1 CH4(g) + H2O(g) Equilibrium 4.1 The equilibrium
  20. November 2021, Paper 1, Q9 (1 mark): An equilibrium system is shown below. CO(g) + NO2(g) CO2(g) + NO(g) Different amounts of CO, NO2, CO2 and NO are added to four containers, as shown below. Conta
  21. November 2021, Paper 1, Q20(a) (1 mark): A dynamic equilibrium exists in a closed system. State one other feature of a dynamic equilibrium. [1]
  22. November 2021, AS Paper 1, Q12 (1 mark): Which statement about dynamic equilibrium is not correct? A A catalyst increases the rate of both forward and reverse reactions by the same amount. B Dynamic eq
  23. November 2021, AS Paper 1, Q22(b) (4 marks): Explain how le Chatelier’s principle can be used to predict the conditions of pressure and temperature for a maximum equilibrium yield of hydrogen in Equilibriu
  24. November 2021, AS Paper 2, Q5(a) (1 mark): Write the expression for the equilibrium constant, Kc, for this equilibrium. [1]
  25. November 2021, AS Paper 2, Q5(b)(i) (2 marks): Calculate the equilibrium concentration of CH3OH(g). concentration = mol dm–3 [2]
  26. November 2021, AS Paper 2, Q5(b)(ii) (1 mark): What does the numerical value of Kc tell you about the position of equilibrium? [1]
  27. November 2020, Paper 1, Q13 (1 mark): Which statement(s) is/are correct when a catalyst is added to a system in dynamic equilibrium? 1 The rates of the forward and reverse reactions increase by the
  28. November 2020, Paper 1, Q17(a) (3 marks): Predict the conditions of pressure and temperature that would give the maximum equilibrium yield of CH3OH in equilibrium 1. Explain your answer. [3]
  29. November 2020, AS Paper 1, Q12 (1 mark): Hydrogen gas can be produced as shown below. CO(g) + 3H2(g) ∆H = +206 kJ mol−1 CH4(g) + H2O(g) Which conditions produce the greatest equilibrium yield of hydrog
  30. November 2020, AS Paper 1, Q13 (1 mark): The reversible reaction below is in equilibrium. 2SO2(g) + O2(g) 2SO3(g) The equilibrium concentrations are shown in the table. Substance SO2(g) O2(g) SO3(g) Eq
  31. November 2020, AS Paper 2, Q4(b)(i) (1 mark): Write the expression for the equilibrium constant, Kc, for this equilibrium. [1]
  32. November 2020, AS Paper 2, Q4(b)(ii) (1 mark): In the equilibrium mixture at 400 °C, the equilibrium concentration of Cl 2(g) is found to be 0.17 mol dm−3. The student calculates that the equilibrium concent
  33. November 2020, AS Paper 2, Q4(b)(iii) (2 marks): At 400 °C, Kc = 0.015 moldm–3. Calculate the equilibrium concentration of NOCl (g) at 400 °C. equilibrium concentration of NOCl (g) = mol dm−3 [2]
  34. November 2020, AS Paper 2, Q4(b)(iv) (2 marks): The temperature of the equilibrium mixture is increased above 400 °C while keeping the pressure constant. State and explain the effect on the equilibrium concen
  35. June 2019, AS Paper 1, Q13 (1 mark): A catalyst is added to a system in equilibrium. What is the effect on the rates of the forward and reverse reactions? A There is no effect on the rate in either
  36. June 2019, AS Paper 1, Q24(a)(i) (4 marks): Explain how le Chatelier’s principle can be used to predict the conditions of temperature and pressure for a maximum equilibrium yield of ammonia. [4]
  37. June 2019, AS Paper 1, Q24(a)(ii) (2 marks): Using certain conditions, equilibrium 24.1 has the equilibrium concentrations in the table. Equilibrium concentration Substance / mol dm−3 N2(g) 1.25 H2(g) 2.75
  38. June 2018, Paper 3, Q2(c)(ii) (2 marks): Explain the observations and predict whether the formation of the blue colour is exothermic or endothermic. [2]
  39. June 2018, AS Paper 1, Q13 (1 mark): The reversible reaction below is at equilibrium. 2SO3(g) ∆H = −197 kJ mol−1 2SO2(g) + O2(g) Which changes in pressure and temperature would shift the equilibriu
  40. June 2018, AS Paper 1, Q14 (1 mark): The reversible reaction below is at equilibrium. N2(g) + 3H2(g) 2NH3(g) What is the expression for Kc? [N2(g)] [H2(g)]3 A [NH3(g)]2 [NH3(g)]2 B [N2(g)] [H2(g)]3
  41. June 2018, AS Paper 2, Q4(b) (1 mark): Write an expression for the equilibrium constant, Kc, in equilibrium 4.1. [1]
  42. June 2018, AS Paper 2, Q4(c) (5 marks): Predict the conditions of temperature and pressure for a maximum equilibrium yield of nitrogen monoxide in equilibrium 4.1. • Explain your prediction in terms o
  43. June 2017, Paper 1, Q20(a) (4 marks): Hydrogen gas is manufactured by the chemical industry using the reaction of methane and steam. This is a reversible reaction, shown in equilibrium 20.1 below. 3
  44. June 2017, AS Paper 1, Q13 (1 mark): The reversible reaction below is allowed to reach equilibrium. ΔH = –9.4 kJ mol–1 H2(g) + I2(g) 2HI(g) Which change in conditions would be expected to shift the
  45. June 2017, AS Paper 1, Q23(c) (2 marks): A chemist investigates the equilibrium that produces methanol: CO(g) + 2H2(g) CH3OH(g) The chemist mixes CO(g) with H2(g) and leaves the mixture to react until
  46. June 2016, AS Paper 1, Q25(a) (5 marks): Le Chatelier’s principle can be used to predict how different conditions affect the equilibrium position. • Using le Chatelier’s principle, show that a low temp
  47. June 2016, AS Paper 1, Q25(b) (4 marks): Under certain conditions, Kc for equilibrium 25.1 is 0.160 dm3 mol–1. The equilibrium mixture under these conditions has the following concentrations of SO2 and

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