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Equilibria: OCR A‑Level Chemistry B questions

Every OCR A-Level Chemistry B exam question on ES Equilibria (specification points ES(o)–(q)), 2016–2025, with its mark scheme and examiner’s report.

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2,049 questions

  1. Q4(b)

    June 2025 · AS Paper 2

    2 marksES Equilibria
    The whole paper ↗
    June 2025 AS Paper 2, question 4(b): Another student wants to measure the equilibrium constant for the reaction between ethanoic acid, CH3COOH, and ethanol, CH3CH2OH. CH3COOH + CH3CH2OH CH3COOCH2CH

  2. Q4(d)(i)

    June 2025 · AS Paper 2

    1 markES Equilibria
    The whole paper ↗
    June 2025 AS Paper 2, question 4(d)(i): Complete the table by calculating the equilibrium concentration of ethanoic acid. Equilibrium amount Equilibrium concentration in 40 cm3 equilibrium mixture in

  3. Q4(d)(ii)

    June 2025 · AS Paper 2

    1 markES Equilibria
    The whole paper ↗
    June 2025 AS Paper 2, question 4(d)(ii): Write the expression for the equilibrium constant for the reaction in Equation 4.1. CH3COOH + CH3CH2OH CH3COOCH2CH3 + H2O Equation 4.1 Kc = [1]

  4. Q4(d)(iii)

    June 2025 · AS Paper 2

    2 marksES Equilibria
    The whole paper ↗
    June 2025 AS Paper 2, question 4(d)(iii): Calculate the numerical value for this equilibrium constant. Give your answer to an appropriate number of significant figures. Numerical value of equilibrium co

  5. Q4(f)

    June 2025 · AS Paper 2

    1 markES Equilibria
    The whole paper ↗
    June 2025 AS Paper 2, question 4(f): Suggest why the student adds the sample of equilibrium mixture to 100 cm3 of ice-cold water before carrying out the titration. [1]

  6. Q4(g)

    June 2025 · AS Paper 2

    3 marksES Equilibria
    The whole paper ↗
    June 2025 AS Paper 2, question 4(g): The student is given some values of the equilibrium constant at various temperatures. As temperature increases, the numerical value of the equilibrium constant

  7. Q33(c)(i)

    June 2024 · Paper 1

    2 marksES Equilibria
    The whole paper ↗
    June 2024 Paper 1, question 33(c)(i): A student says that once the position of equilibrium has been reached, the reaction has stopped so the concentration of NO2(g) remains constant. Evaluate what t

  8. Q33(c)(ii)

    June 2024 · Paper 1

    3 marksES Equilibria
    The whole paper ↗
    June 2024 Paper 1, question 33(c)(ii): For the reaction in Equation 33.1 at a certain temperature, Kc = 6.9 × 102 dm3 mol–1 In an industrial plant, operating at that temperature: Equilibrium concentr

  9. Q12

    June 2024 · AS Paper 1

    1 markES Equilibria
    The whole paper ↗
    June 2024 AS Paper 1, question 12: A reaction has a Kc11 1 × 10–10 What is correct for this reaction? A Concentration of products = concentration of reactants. B It forms an equilibrium with more

  10. Q4(a)(i)

    June 2024 · AS Paper 2

    1 markES Equilibria
    The whole paper ↗
    June 2024 AS Paper 2, question 4(a)(i): Write the expression for the Kc for the equilibrium in Equation 4.1. [1]

  11. Q4(a)(ii)

    June 2024 · AS Paper 2

    2 marksES Equilibria
    The whole paper ↗
    June 2024 AS Paper 2, question 4(a)(ii): At a certain temperature, the numerical value of Kc for the equilibrium shown in Equation 4.1 is 285. In an equilibrium mixture at this temperature, [N2O4] = 4.

  12. Q4(a)(iii)

    June 2024 · AS Paper 2

    3 marksES Equilibria
    The whole paper ↗
    June 2024 AS Paper 2, question 4(a)(iii): The equilibrium is then set up at a higher temperature. Will the value of Kc increase, decrease or stay the same? Explain your answer. [3]

  13. Q4(b)

    June 2024 · AS Paper 2

    6 marksES Equilibria
    The whole paper ↗
    June 2024 AS Paper 2, question 4(b): A student investigates the equilibrium in Equation 4.1. N2O4(g) ΔH = –58 kJ mol–1 Equation 4.1 2NO2(g) NO2(g) is brown and N2O4(g) is colourless. (b)* The stude

  14. Q7

    June 2023 · Paper 1

    1 markES Equilibria
    The whole paper ↗
    June 2023 Paper 1, question 7: A student studies a reaction that ‘goes to completion’. The student estimates the numerical value of Kc for the reaction. What is a valid estimate for Kc for th

  15. Q4(a)

    June 2023 · AS Paper 2

    3 marksES Equilibria
    The whole paper ↗
    June 2023 AS Paper 2, question 4(a): A student says: • When a reaction is in dynamic equilibrium, the forward and reverse reactions have stopped. • This means that the concentrations of reactants a

  16. Q4(b)

    June 2023 · AS Paper 2

    3 marksES Equilibria
    The whole paper ↗
    June 2023 AS Paper 2, question 4(b): For the equilibrium in Equation 4.1: [NH3]2 Kc = [N2] [H2]3 At a temperature of 472 K, this equilibrium constant has a numerical value of 0.105. In an equilibri

  17. Q34(a)

    June 2022 · Paper 1

    2 marksES Equilibria
    The whole paper ↗
    June 2022 Paper 1, question 34(a): Student F says that dynamic equilibrium is reached when the forward and back reactions are still occurring and the concentrations of the reactants and products

  18. Q34(b)(i)

    June 2022 · Paper 1

    1 markES Equilibria
    The whole paper ↗
    June 2022 Paper 1, question 34(b)(i): Write the expression for the equilibrium constant Kc for the reaction in Equation 34.1. Kc = [1]

  19. Q34(b)(ii)

    June 2022 · Paper 1

    4 marksES Equilibria
    The whole paper ↗
    June 2022 Paper 1, question 34(b)(ii): The value of Kc at 657 K is 4.75 × 103 dm6 mol–2. The reaction in Equation 34.1 is carried out at 657 K in a flask of volume 9.40 × 103 cm3. An equilibrium mixt

  20. Q24(a)

    June 2022 · AS Paper 1

    2 marksES Equilibria
    The whole paper ↗
    June 2022 AS Paper 1, question 24(a): The reaction is in dynamic equilibrium. Describe what is happening to the concentrations of the gases and the rates of the forward and back reactions at equilib
All 49 questions on Equilibria, as a list
  1. June 2025, AS Paper 2, Q4(b) (2 marks): Another student wants to measure the equilibrium constant for the reaction between ethanoic acid, CH3COOH, and ethanol, CH3CH2OH. CH3COOH + CH3CH2OH CH3COOCH2CH
  2. June 2025, AS Paper 2, Q4(d)(i) (1 mark): Complete the table by calculating the equilibrium concentration of ethanoic acid. Equilibrium amount Equilibrium concentration in 40 cm3 equilibrium mixture in
  3. June 2025, AS Paper 2, Q4(d)(ii) (1 mark): Write the expression for the equilibrium constant for the reaction in Equation 4.1. CH3COOH + CH3CH2OH CH3COOCH2CH3 + H2O Equation 4.1 Kc = [1]
  4. June 2025, AS Paper 2, Q4(d)(iii) (2 marks): Calculate the numerical value for this equilibrium constant. Give your answer to an appropriate number of significant figures. Numerical value of equilibrium co
  5. June 2025, AS Paper 2, Q4(f) (1 mark): Suggest why the student adds the sample of equilibrium mixture to 100 cm3 of ice-cold water before carrying out the titration. [1]
  6. June 2025, AS Paper 2, Q4(g) (3 marks): The student is given some values of the equilibrium constant at various temperatures. As temperature increases, the numerical value of the equilibrium constant
  7. June 2024, Paper 1, Q33(c)(i) (2 marks): A student says that once the position of equilibrium has been reached, the reaction has stopped so the concentration of NO2(g) remains constant. Evaluate what t
  8. June 2024, Paper 1, Q33(c)(ii) (3 marks): For the reaction in Equation 33.1 at a certain temperature, Kc = 6.9 × 102 dm3 mol–1 In an industrial plant, operating at that temperature: Equilibrium concentr
  9. June 2024, AS Paper 1, Q12 (1 mark): A reaction has a Kc11 1 × 10–10 What is correct for this reaction? A Concentration of products = concentration of reactants. B It forms an equilibrium with more
  10. June 2024, AS Paper 2, Q4(a)(i) (1 mark): Write the expression for the Kc for the equilibrium in Equation 4.1. [1]
  11. June 2024, AS Paper 2, Q4(a)(ii) (2 marks): At a certain temperature, the numerical value of Kc for the equilibrium shown in Equation 4.1 is 285. In an equilibrium mixture at this temperature, [N2O4] = 4.
  12. June 2024, AS Paper 2, Q4(a)(iii) (3 marks): The equilibrium is then set up at a higher temperature. Will the value of Kc increase, decrease or stay the same? Explain your answer. [3]
  13. June 2024, AS Paper 2, Q4(b) (6 marks): A student investigates the equilibrium in Equation 4.1. N2O4(g) ΔH = –58 kJ mol–1 Equation 4.1 2NO2(g) NO2(g) is brown and N2O4(g) is colourless. (b)* The stude
  14. June 2023, Paper 1, Q7 (1 mark): A student studies a reaction that ‘goes to completion’. The student estimates the numerical value of Kc for the reaction. What is a valid estimate for Kc for th
  15. June 2023, AS Paper 2, Q4(a) (3 marks): A student says: • When a reaction is in dynamic equilibrium, the forward and reverse reactions have stopped. • This means that the concentrations of reactants a
  16. June 2023, AS Paper 2, Q4(b) (3 marks): For the equilibrium in Equation 4.1: [NH3]2 Kc = [N2] [H2]3 At a temperature of 472 K, this equilibrium constant has a numerical value of 0.105. In an equilibri
  17. June 2022, Paper 1, Q34(a) (2 marks): Student F says that dynamic equilibrium is reached when the forward and back reactions are still occurring and the concentrations of the reactants and products
  18. June 2022, Paper 1, Q34(b)(i) (1 mark): Write the expression for the equilibrium constant Kc for the reaction in Equation 34.1. Kc = [1]
  19. June 2022, Paper 1, Q34(b)(ii) (4 marks): The value of Kc at 657 K is 4.75 × 103 dm6 mol–2. The reaction in Equation 34.1 is carried out at 657 K in a flask of volume 9.40 × 103 cm3. An equilibrium mixt
  20. June 2022, AS Paper 1, Q24(a) (2 marks): The reaction is in dynamic equilibrium. Describe what is happening to the concentrations of the gases and the rates of the forward and back reactions at equilib
  21. June 2022, AS Paper 1, Q24(b) (2 marks): The concentration of N2O4 starts at 1.0 mol dm–3 and reaches equilibrium again at 0.40 mol dm–3. Sketch a line on the axes above to show how the concentration o
  22. June 2022, AS Paper 1, Q24(c) (2 marks): Use data from the graph to calculate the numerical value of Kc for the equilibrium in equation 24.1 at 600 K. Kc value = [2]
  23. June 2022, AS Paper 1, Q24(d) (2 marks): Use equation 24.1 to explain why more NO2 is formed at 600 K, compared with 298 K. [2]
  24. November 2021, AS Paper 2, Q4(a) (3 marks): The reaction represented by Equation 4.1 can reach a position of dynamic equilibrium. A student says that a position of dynamic equilibrium is reached when the
  25. November 2021, AS Paper 2, Q4(b)(i) (1 mark): Write an expression for the equilibrium constant, Kc, for the reaction shown in Equation 4.1. [1]
  26. November 2021, AS Paper 2, Q4(b)(ii) (2 marks): At a temperature of 480 K, the reaction shown in Equation 4.1 has the following equilibrium concentrations. Equilibrium concentration / mol dm–3 Substance CH3OH
  27. November 2021, AS Paper 2, Q4(c) (6 marks): Methanol can be used as a fuel. It can be made industrially by the catalysed reaction between carbon monoxide and hydrogen as shown in Equation 4.1. CH3OH(g) ΔH
  28. November 2020, Paper 1, Q4 (1 mark): Reversible reactions reach dynamic equilibrium. What is correct about these equilibria? A They must be set up in a closed system. B The overall concentrations r
  29. November 2020, Paper 2, Q3(d) (2 marks): The acidity of KH2PO4 reduces the loss of ammonia from ammonium ions (NH4 Explain how this happens when the fertiliser is in solution. [2]
  30. November 2020, AS Paper 1, Q24(a) (2 marks): Plot the data in the table on the axes below. Draw a line of best fit. Label this line ‘Moles H2’. [2] 3.5 3 2.5 2 amount / mol 1.5 1 Moles CO 0.5 Moles CH4 = M
  31. November 2020, AS Paper 1, Q24(b) (3 marks): The graphs show that the reaction has reached equilibrium after 40 minutes. The volume of the container for the experiment is 1.0 dm3. Use data from the graph t
  32. November 2020, AS Paper 1, Q24(c) (2 marks): The pressure is increased on the equilibrium in equation 24.1. The volume remains the same. Sketch on the graph, on page 16, a line for ‘moles CO at a higher pr
  33. June 2019, Paper 1, Q24 (1 mark): The reaction for the formation of sulfur trioxide is shown below. 2SO2(g) + O2(g) 2SO3(g) 60 cm3 of sulfur dioxide are mixed with 60 cm3 of oxygen and allowed t
  34. June 2019, Paper 1, Q31(a) (2 marks): The reaction can be allowed to reach dynamic equilibrium. Explain what is meant by dynamic equilibrium. [2]
  35. June 2019, Paper 1, Q31(b) (3 marks): At a certain temperature, the equilibrium constant, Kc, for the reaction in equation 31.1 is 3.0 dm6 mol–2. In an equilibrium mixture, the concentrations of nit
  36. June 2019, Paper 1, Q31(c) (2 marks): A Chemist says the process would be more efficient if the ammonia produced is continuously liquefied and removed from the reaction vessel. Comment on the Chemis
  37. June 2019, AS Paper 1, Q21(b) (1 mark): State what is happening to the forward and reverse reactions once equilibrium has been reached. [1]
  38. June 2019, AS Paper 1, Q21(c)(i) (3 marks): On the graph paper below plot the results in Table 21.1 and draw lines of best fit. [3]
  39. June 2019, AS Paper 1, Q21(c)(ii) (2 marks): How would the plot for 673 K be different if the iron catalyst had not been used? Explain your answer. [2]
  40. June 2019, AS Paper 1, Q21(c)(iii) (1 mark): Explain why the yield is greater at higher pressures. [1]
  41. June 2019, AS Paper 1, Q21(c)(iv) (2 marks): A student says that an industrial firm carrying out the reaction at 473 K would not use a pressure above 400 atmospheres. Discuss the student’s statement, givin
  42. June 2019, AS Paper 1, Q21(d) (2 marks): The equilibrium shown in equation 1.1 is set up. The data below shows the composition of an equilibrium mixture at 473 K. Equilibrium concentration / mol dm–3 E
  43. June 2018, AS Paper 1, Q24(d)(i) (1 mark): Complete the expression for the equilibrium constant, Kc, for this reaction. Kc = [1]
  44. June 2018, AS Paper 1, Q24(d)(ii) (2 marks): A student says that, when equilibrium is reached in equation 24.1: • the rates of the forward and back reactions are equal • the concentrations of NO, O2 and NO
  45. June 2018, AS Paper 1, Q24(d)(iii) (5 marks): Consider and explain the conditions of temperature and pressure that would give the greatest equilibrium yield of NO in equation 24.1. [5]
  46. June 2017, Paper 2, Q4(c)(ii) (2 marks): Some students have a violet solution of chromium(III) chloride. Use your knowledge of equilibria to suggest and explain how they might make the violet solution
  47. June 2017, AS Paper 1, Q24(a) (1 mark): Ethyl ethanoate can be made in the laboratory by the reaction shown below. CH3COOH + C2H5OH CH3COOC2H5 + H2O This reaction can reach dynamic equilibrium. What c
  48. June 2016, AS Paper 1, Q4 (1 mark): Ammonia is made by the reaction shown below. 2NH3 ΔH = −92 kJ mol−1 N2 + 3H2 Which conditions will result in the greatest equilibrium yield of ammonia? Temperat
  49. June 2016, AS Paper 1, Q14 (1 mark): The following data were collected for the equilibrium H2(g) + I2(g) 2HI(g) at 500 K. [HI(g)]2 eqm [H2 (g)]eqm = 0.14 mol dm−3 [I2 (g)]eqm = 0.040 mol dm−3 Kc =

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