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Rates of reaction: WJEC A‑Level Chemistry questions

Every WJEC A-Level Chemistry exam question on 2.2 Rates of reaction, 2016–2025, with its mark scheme and examiner’s report.

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1,204 questions

  1. Q3(a)

    Summer 2025 · Unit 3

    1 mark2.2 Rates of reaction
    The whole paper ↗
    Summer 2025 Unit 3, question 3(a): State what is meant by the term heterogeneous in this context. [1]

  2. Q3(b)

    Summer 2025 · Unit 3

    1 mark2.2 Rates of reaction
    The whole paper ↗
    Summer 2025 Unit 3, question 3(b): Give an example of a heterogeneous catalyst and the reaction it catalyses. [1]

  3. Q6(d)(ii)

    Summer 2025 · Unit 4

    2 marks2.2 Rates of reaction
    The whole paper ↗
    Summer 2025 Unit 4, question 6(d)(ii): This reaction is quite slow. Suggest two ways by which the rate of this reaction could be studied. [2]

  4. Q3(a)

    Summer 2025 · AS Unit 2

    1 mark2.2 Rates of reaction
    The whole paper ↗
    Summer 2025 AS Unit 2, question 3(a): The diagram below shows the Boltzmann energy distribution curve for a reaction at 298 K. Number of particles Energy On the diagram, draw the curve for the same

  5. Q3(b)

    Summer 2025 · AS Unit 2

    1 mark2.2 Rates of reaction
    The whole paper ↗
    Summer 2025 AS Unit 2, question 3(b): State how a catalyst increases the rate of a reaction. [1]

  6. Q8(a)

    Summer 2025 · AS Unit 2

    1 mark2.2 Rates of reaction
    The whole paper ↗
    Summer 2025 AS Unit 2, question 8(a): Complete the reaction profile below to show the enthalpy change involved in an endothermic reaction. Label the enthalpy change clearly on the diagram. [1] Energ

  7. Q11(a)(iii)

    Summer 2025 · AS Unit 2

    2 marks2.2 Rates of reaction
    The whole paper ↗
    Summer 2025 AS Unit 2, question 11(a)(iii): Calculate the mean rate of the reaction shown by graph B. Give the appropriate unit. [2] Rate = Unit

  8. Q11(a)(iv)

    Summer 2025 · AS Unit 2

    1 mark2.2 Rates of reaction
    The whole paper ↗
    Summer 2025 AS Unit 2, question 11(a)(iv): Using the graphs, suggest why the results of this experiment could be considered to be not valid. [1]

  9. Q11(b)

    Summer 2025 · AS Unit 2

    6 marks2.2 Rates of reaction
    The whole paper ↗
    Summer 2025 AS Unit 2, question 11(b): Another student investigated the effect of concentration on rate using an iodine clock reaction. This method uses a solution containing persulfate ions to oxidi

  10. Q8(d)(i)

    Summer 2024 · Unit 3

    1 mark2.2 Rates of reaction
    The whole paper ↗
    Summer 2024 Unit 3, question 8(d)(i): State what is meant by the term heterogeneous in this context. [1]

  11. Q2

    Summer 2024 · AS Unit 2

    2 marks2.2 Rates of reaction
    The whole paper ↗
    Summer 2024 AS Unit 2, question 2: Draw the energy profile diagram for an endothermic reaction. Label the activation energy, Ea, and the enthalpy change of the reaction, ΔH. [2] Energy Progress o

  12. Q10(a)

    Summer 2024 · AS Unit 2

    4 marks2.2 Rates of reaction
    The whole paper ↗
    Summer 2024 AS Unit 2, question 10(a): Describe how the student could prepare 250 cm3 of 0.10 mol dm–3 sodium thiosulfate solution to use in this experiment. The relative formula mass (Mr ) of sodium

  13. Q10(b)(i)

    Summer 2024 · AS Unit 2

    1 mark2.2 Rates of reaction
    The whole paper ↗
    Summer 2024 AS Unit 2, question 10(b)(i): State what causes the cross to become obscured. [1]

  14. Q10(b)(ii)

    Summer 2024 · AS Unit 2

    1 mark2.2 Rates of reaction
    The whole paper ↗
    Summer 2024 AS Unit 2, question 10(b)(ii): The diagram shows a beaker and a shallow dish. If the student replaced the beaker with a shallow dish, state the effect this would have on the time taken to obs

  15. Q10(c)(i)

    Summer 2024 · AS Unit 2

    2 marks2.2 Rates of reaction
    The whole paper ↗
    Summer 2024 AS Unit 2, question 10(c)(i): Complete the table to show suitable volumes of thiosulfate, water and acid that the student could use to investigate the effect of changing concentration of S2O

  16. Q10(c)(ii)

    Summer 2024 · AS Unit 2

    1 mark2.2 Rates of reaction
    The whole paper ↗
    Summer 2024 AS Unit 2, question 10(c)(ii): The rate of reaction can be calculated using rate = time State the unit of rate in this reaction. [1]

  17. Q10(c)(iii)

    Summer 2024 · AS Unit 2

    1 mark2.2 Rates of reaction
    The whole paper ↗
    Summer 2024 AS Unit 2, question 10(c)(iii): The student calculates the rate of reaction using different volumes of S2O32–(aq) and plots a graph. The graph is shown. Rate 0 Volume S2O32–(aq) / cm3 State wh

  18. Q10(d)(i)

    Summer 2024 · AS Unit 2

    2 marks2.2 Rates of reaction
    The whole paper ↗
    Summer 2024 AS Unit 2, question 10(d)(i): Use the graph to determine the time taken for the cross to be obscured at a temperature of 30 °C. Show clearly how you obtained your answer. [2] rate = 1000 tim

  19. Q10(d)(ii)

    Summer 2024 · AS Unit 2

    2 marks2.2 Rates of reaction
    The whole paper ↗
    Summer 2024 AS Unit 2, question 10(d)(ii): Some textbooks state that a 10 °C temperature rise approximately doubles the rate of many reactions. Use the graph to find to what extent this is true for this

  20. Q10(d)(iii)

    Summer 2024 · AS Unit 2

    2 marks2.2 Rates of reaction
    The whole paper ↗
    Summer 2024 AS Unit 2, question 10(d)(iii): Explain why the rate of the reaction is affected by an increase in temperature. [2]
All 56 questions on Rates of reaction, as a list
  1. Summer 2025, Unit 3, Q3(a) (1 mark): State what is meant by the term heterogeneous in this context. [1]
  2. Summer 2025, Unit 3, Q3(b) (1 mark): Give an example of a heterogeneous catalyst and the reaction it catalyses. [1]
  3. Summer 2025, Unit 4, Q6(d)(ii) (2 marks): This reaction is quite slow. Suggest two ways by which the rate of this reaction could be studied. [2]
  4. Summer 2025, AS Unit 2, Q3(a) (1 mark): The diagram below shows the Boltzmann energy distribution curve for a reaction at 298 K. Number of particles Energy On the diagram, draw the curve for the same
  5. Summer 2025, AS Unit 2, Q3(b) (1 mark): State how a catalyst increases the rate of a reaction. [1]
  6. Summer 2025, AS Unit 2, Q8(a) (1 mark): Complete the reaction profile below to show the enthalpy change involved in an endothermic reaction. Label the enthalpy change clearly on the diagram. [1] Energ
  7. Summer 2025, AS Unit 2, Q11(a)(iii) (2 marks): Calculate the mean rate of the reaction shown by graph B. Give the appropriate unit. [2] Rate = Unit
  8. Summer 2025, AS Unit 2, Q11(a)(iv) (1 mark): Using the graphs, suggest why the results of this experiment could be considered to be not valid. [1]
  9. Summer 2025, AS Unit 2, Q11(b) (6 marks): Another student investigated the effect of concentration on rate using an iodine clock reaction. This method uses a solution containing persulfate ions to oxidi
  10. Summer 2024, Unit 3, Q8(d)(i) (1 mark): State what is meant by the term heterogeneous in this context. [1]
  11. Summer 2024, AS Unit 2, Q2 (2 marks): Draw the energy profile diagram for an endothermic reaction. Label the activation energy, Ea, and the enthalpy change of the reaction, ΔH. [2] Energy Progress o
  12. Summer 2024, AS Unit 2, Q10(a) (4 marks): Describe how the student could prepare 250 cm3 of 0.10 mol dm–3 sodium thiosulfate solution to use in this experiment. The relative formula mass (Mr ) of sodium
  13. Summer 2024, AS Unit 2, Q10(b)(i) (1 mark): State what causes the cross to become obscured. [1]
  14. Summer 2024, AS Unit 2, Q10(b)(ii) (1 mark): The diagram shows a beaker and a shallow dish. If the student replaced the beaker with a shallow dish, state the effect this would have on the time taken to obs
  15. Summer 2024, AS Unit 2, Q10(c)(i) (2 marks): Complete the table to show suitable volumes of thiosulfate, water and acid that the student could use to investigate the effect of changing concentration of S2O
  16. Summer 2024, AS Unit 2, Q10(c)(ii) (1 mark): The rate of reaction can be calculated using rate = time State the unit of rate in this reaction. [1]
  17. Summer 2024, AS Unit 2, Q10(c)(iii) (1 mark): The student calculates the rate of reaction using different volumes of S2O32–(aq) and plots a graph. The graph is shown. Rate 0 Volume S2O32–(aq) / cm3 State wh
  18. Summer 2024, AS Unit 2, Q10(d)(i) (2 marks): Use the graph to determine the time taken for the cross to be obscured at a temperature of 30 °C. Show clearly how you obtained your answer. [2] rate = 1000 tim
  19. Summer 2024, AS Unit 2, Q10(d)(ii) (2 marks): Some textbooks state that a 10 °C temperature rise approximately doubles the rate of many reactions. Use the graph to find to what extent this is true for this
  20. Summer 2024, AS Unit 2, Q10(d)(iii) (2 marks): Explain why the rate of the reaction is affected by an increase in temperature. [2]
  21. Summer 2023, Unit 3, Q6 (1 mark): The Haber process uses a heterogeneous catalyst. State what is meant by the term ‘heterogeneous’ in this context. [1]
  22. Summer 2023, AS Unit 2, Q6 (1 mark): In the forward direction, the enthalpy change of reaction, ΔH, for a reversible endothermic reaction, has the numerical value of 60 kJ mol–1. If the activation
  23. Summer 2023, AS Unit 2, Q9(a)(i) (2 marks): The students calculated that the initial rate of the reaction was 1.20 mol dm–3 min–1. Use the tangent to the curve to calculate the rate of the reaction when t
  24. Summer 2023, AS Unit 2, Q9(a)(ii) (1 mark): Use your answer to part (i) to suggest the relationship between the rate of this reaction and the concentration of bromide ions. [1]
  25. Summer 2023, AS Unit 2, Q9(b) (2 marks): Suggest how the students could follow the rate of this reaction. Explain your answer. [2]
  26. Summer 2023, AS Unit 2, Q9(c) (1 mark): over the first 4 minutes. The initial concentration of bromate(V) ions was 1.0 moldm–3. 5Br–(aq) –(aq) 6H+(aq) 3Br2(aq) 3H2O(I) BrO3 + + + Using the equation, d
  27. Summer 2022, AS Unit 2, Q9(a) (1 mark): The violet complex appears black at the beginning of the reaction. State the name of the technique used to monitor the rate of reaction by measuring the absorpt
  28. Summer 2022, AS Unit 2, Q9(b)(i) (2 marks): State which catalyst is the most effective. Explain your answer. [2]
  29. Summer 2022, AS Unit 2, Q9(b)(ii) (2 marks): Calculate the initial rate of reaction for the reaction catalysed by the copper(II) ions. [2] rate = s–1
  30. Summer 2022, AS Unit 2, Q9(b)(iii) (1 mark): Each catalysed reaction contained the same number of moles of catalyst at the beginning of the reaction. Calculate the moles of catalyst left at the end of the
  31. Summer 2022, AS Unit 2, Q9(c) (6 marks): Increasing temperature and the addition of a catalyst are two ways of increasing the rate of a reaction. Using your knowledge of the Boltzmann distribution and
  32. Summer 2019, AS Unit 2, Q8(a) (2 marks): Explain why a change in concentration affects the rate of a reaction. [2]
  33. Summer 2019, AS Unit 2, Q8(b)(i) (2 marks): Use the data to determine how the concentration of NO affects the rate of the reaction. Explain your answer by referring to the experiment numbers. [2]
  34. Summer 2019, AS Unit 2, Q8(b)(ii) (2 marks): Use the data to determine how the concentration of O2 affects the rate of the reaction. Explain your answer by referring to the experiment numbers. [2]
  35. Summer 2019, AS Unit 2, Q8(b)(iii) (2 marks): Suggest a method that could be used to follow changes over time as the reaction of nitrogen monoxide, carbon monoxide and oxygen proceeds. Explain your answer.
  36. Summer 2019, AS Unit 2, Q8(b)(v) (2 marks): The reaction shown is one of many that are catalysed in a catalytic converter. State where in a car a catalytic converter is used and name a suitable catalyst.
  37. Summer 2019, AS Unit 2, Q8(c) (3 marks): On the axes below draw a Boltzmann distribution curve of the energies of molecules at a certain temperature. Use this curve to explain how a catalyst increases
  38. Summer 2018, Unit 3, Q11(a) (1 mark): The rate of decomposition of hydrogen peroxide can be influenced by a range of catalysts. The activation energy when using MnO2 as a catalyst is 58 kJ mol–1. Dr
  39. Summer 2018, AS Unit 2, Q9(a)(iii) (2 marks): Use your answer to part (ii) to sketch an energy profile diagram for this reaction on the axes below. Label ΔH and the activation energy, Ea, on your diagram. [
  40. Summer 2018, AS Unit 2, Q12(a)(i) (1 mark): time to calculate the rate for each experiment and complete the table. [1]
  41. Summer 2018, AS Unit 2, Q12(a)(ii) (3 marks): line. [3]
  42. Summer 2018, AS Unit 2, Q12(a)(iii) (1 mark): reaction. [1]
  43. Summer 2018, AS Unit 2, Q12(a)(iv) (2 marks): Use the graph to calculate the time the reaction would take to turn blue-black using a 0.15 mol dm–3 solution of I–. Show clearly how you obtained your answer.
  44. Summer 2018, AS Unit 2, Q12(a)(v) (2 marks): For each experiment the rate was calculated using the time taken to produce excess iodine. Explain why this is only an approximation for the rate as the reactio
  45. Summer 2018, AS Unit 2, Q12(b)(i) (2 marks): Draw a Boltzmann energy distribution curve. Label the axes. [2]
  46. Summer 2018, AS Unit 2, Q12(b)(ii) (2 marks): Use this energy distribution curve to explain how catalysts affect the rate of a reaction. [2]
  47. Summer 2017, AS Unit 2, Q3 (2 marks): The diagram shows the distribution of the energies of particles in a gas at a particular temperature. Number of particles Ea Energy On the diagram draw a curve
  48. Summer 2017, AS Unit 2, Q9(a) (2 marks): Draw a labelled diagram of the apparatus he could use to carry out the experiment and measure the volume of oxygen produced. [2]
  49. Summer 2017, AS Unit 2, Q9(b)(i) (2 marks): Use the graph to calculate the initial rate of the reaction. Show clearly, on your graph, how you obtained your answer. [2] Initial rate = cm3 s–1
  50. Summer 2017, AS Unit 2, Q9(b)(ii) (1 mark): Use the graph to calculate the rate of the reaction at 200 seconds. Show clearly, on your graph, how you obtained your answer. [1] Rate = cm3 s–1
  51. Summer 2017, AS Unit 2, Q9(b)(iii) (2 marks): Use collision theory to explain why the rates you have calculated in parts (i) and (ii) are different. [2]
  52. Summer 2017, AS Unit 2, Q9(b)(iv) (3 marks): solution used by the student. Give your answer correct to three significant figures. [3] Assume that the reaction was carried out at 298 K and 1 atm pressure. C
  53. Summer 2017, AS Unit 2, Q9(c) (3 marks): A second student said that she had seen cobalt(II) chloride speed up the rate of production of oxygen very significantly in a different reaction. Describe how t
  54. Summer 2016, AS Unit 2, Q2 (2 marks): Respiration involves the release of energy by using foods. The equation for the respiration of glucose is shown below. C6H12O6 + 6O2 6CO2 + 6H2O ΔH = –2900 kJ m
  55. Summer 2016, AS Unit 2, Q4 (2 marks): Bromine reacts with methanoic acid according to the equation below. Br2(aq) + HCOOH(aq) 2Br –(aq) + 2H+(aq) + CO2(g) A student wanted to follow the rate of the
  56. Summer 2016, AS Unit 2, Q10(b)(i) (2 marks): Use these data to deduce how the concentration of each reagent affects the rate of reaction. Explain how you reached your conclusions. [2]

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