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Entropy and feasibility of reactions: WJEC A‑Level Chemistry questions

Every WJEC A-Level Chemistry exam question on 3.7 Entropy and feasibility of reactions, 2016–2025, with its mark scheme and examiner’s report.

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1,204 questions

  1. Q7(a)(i)

    Summer 2025 · Unit 3

    1 mark3.7 Entropy and feasibility of reactions
    The whole paper ↗
    Summer 2025 Unit 3, question 7(a)(i): Give a reason why all the entropy changes are positive. [1]

  2. Q7(a)(ii)

    Summer 2025 · Unit 3

    3 marks3.7 Entropy and feasibility of reactions
    The whole paper ↗
    Summer 2025 Unit 3, question 7(a)(ii): The minimum temperature for decomposition of calcium nitrate is 1500 °C. Find the standard enthalpy change for this reaction. [3] kJ mol–1 Standard enthalpy cha

  3. Q8(d)(ii)

    Summer 2024 · Unit 3

    9 marks3.7 Entropy and feasibility of reactions2.1 Thermochemistry
    The whole paper ↗
    Summer 2024 Unit 3, question 8(d)(ii): This catalyst is used to catalyse the oxidation of sulfur dioxide. ΔHθ = –197 kJ mol–1 2SO2(g) + O2(g) 2SO3(g) ΔSθ = –187 J K–1 mol–1 The standard enthalpy chan

  4. Q10(c)(ii)

    Summer 2024 · Unit 3

    6 marks3.7 Entropy and feasibility of reactions3.4 Chemistry of the d-block transition metals
    The whole paper ↗
    Summer 2024 Unit 3, question 10(c)(ii): aqueous solution. [Cu(NH3)4(H2O)2]2+(aq) [Cu(cyclen)(H2O)2]2+(aq) + cyclen(aq) + 4NH3(aq) ΔHθ = +1.2 kJ mol–1 Measurements show that the strengths of the Cu―N b

  5. Q8(d)(ii)

    Summer 2023 · Unit 3

    2 marks3.7 Entropy and feasibility of reactions
    The whole paper ↗
    Summer 2023 Unit 3, question 8(d)(ii): Calculate the minimum temperature required for this reaction. [2] minimum temperature = K

  6. Q10(a)

    Summer 2023 · Unit 3

    3 marks3.7 Entropy and feasibility of reactions
    The whole paper ↗
    Summer 2023 Unit 3, question 10(a): Some thermodynamic data for F2O and Cl2O are given below. Standard enthalpy change of Standard molar entropy, Substance formation, ∆fHθ / kJ mol−1 Sθ / J K−1 mo

  7. Q7

    Summer 2022 · Unit 3

    1 mark3.7 Entropy and feasibility of reactions
    The whole paper ↗
    Summer 2022 Unit 3, question 7: Give a reason why the entropy of Hg(l) is greater than that of Au(s). [1]

  8. Q8(b)(iii)

    Summer 2022 · Unit 3

    2 marks3.7 Entropy and feasibility of reactions
    The whole paper ↗
    Summer 2022 Unit 3, question 8(b)(iii): A student suggests that the entropy change for the formation of sodium chloride must be positive as the reaction occurs easily. Is the student correct? Justify

  9. Q10(e)

    Summer 2022 · Unit 3

    3 marks3.7 Entropy and feasibility of reactions3.9 Acid-base equilibria
    The whole paper ↗
    Summer 2022 Unit 3, question 10(e): Some data regarding the dissociation of another weak acid, HX, at two different temperatures are given in the table. H+ X– HX + HX HX at 298 K at temperature T

  10. Q6

    Summer 2019 · Unit 3

    1 mark3.7 Entropy and feasibility of reactions
    The whole paper ↗
    Summer 2019 Unit 3, question 6: The entropy change of the reaction shown below is positive. Give a reason for this. [1] Na2CO3(aq) + 2HCl(aq) 2NaCl(aq) + CO2(g) + H2O(l)

  11. Q9(b)(i)

    Summer 2019 · Unit 3

    3 marks3.7 Entropy and feasibility of reactions
    The whole paper ↗
    Summer 2019 Unit 3, question 9(b)(i): A laboratory manual suggests a minimum temperature of 200 °C to remove all the water from the hydrated calcium chloride. At this temperature the reaction occurr

  12. Q6

    Summer 2018 · Unit 3

    1 mark3.7 Entropy and feasibility of reactions
    The whole paper ↗
    Summer 2018 Unit 3, question 6: The enthalpy of solution of sodium chloride is +4 kJ mol–1. Explain why this compound is soluble 6 in water despite this value being positive. [1]

  13. Q11(d)

    Summer 2018 · Unit 3

    1 mark3.7 Entropy and feasibility of reactions
    The whole paper ↗
    Summer 2018 Unit 3, question 11(d): State whether you would expect the entropy change for the decomposition of hydrogen peroxide to be positive or negative. Give a reason for your answer. [1]

  14. Q6

    Summer 2017 · Unit 3

    1 mark3.7 Entropy and feasibility of reactions
    The whole paper ↗
    Summer 2017 Unit 3, question 6: Place the following substances in order of increasing entropy under standard conditions. [1] nitrogen gas copper metal water air Lowest Highest

  15. Q10(d)(i)

    Summer 2017 · Unit 3

    3 marks3.7 Entropy and feasibility of reactions
    The whole paper ↗
    Summer 2017 Unit 3, question 10(d)(i): [3] ΔGθ = kJ mol−1

  16. Q10(d)(ii)

    Summer 2017 · Unit 3

    1 mark3.7 Entropy and feasibility of reactions
    The whole paper ↗
    Summer 2017 Unit 3, question 10(d)(ii): An alternative method of preparing aqua regia is to use concentrated hydrochloric acid with concentrated nitric acid. State, giving a reason, the effect of this
All 16 questions on Entropy and feasibility of reactions, as a list
  1. Summer 2025, Unit 3, Q7(a)(i) (1 mark): Give a reason why all the entropy changes are positive. [1]
  2. Summer 2025, Unit 3, Q7(a)(ii) (3 marks): The minimum temperature for decomposition of calcium nitrate is 1500 °C. Find the standard enthalpy change for this reaction. [3] kJ mol–1 Standard enthalpy cha
  3. Summer 2024, Unit 3, Q8(d)(ii) (9 marks): This catalyst is used to catalyse the oxidation of sulfur dioxide. ΔHθ = –197 kJ mol–1 2SO2(g) + O2(g) 2SO3(g) ΔSθ = –187 J K–1 mol–1 The standard enthalpy chan
  4. Summer 2024, Unit 3, Q10(c)(ii) (6 marks): aqueous solution. [Cu(NH3)4(H2O)2]2+(aq) [Cu(cyclen)(H2O)2]2+(aq) + cyclen(aq) + 4NH3(aq) ΔHθ = +1.2 kJ mol–1 Measurements show that the strengths of the Cu―N b
  5. Summer 2023, Unit 3, Q8(d)(ii) (2 marks): Calculate the minimum temperature required for this reaction. [2] minimum temperature = K
  6. Summer 2023, Unit 3, Q10(a) (3 marks): Some thermodynamic data for F2O and Cl2O are given below. Standard enthalpy change of Standard molar entropy, Substance formation, ∆fHθ / kJ mol−1 Sθ / J K−1 mo
  7. Summer 2022, Unit 3, Q7 (1 mark): Give a reason why the entropy of Hg(l) is greater than that of Au(s). [1]
  8. Summer 2022, Unit 3, Q8(b)(iii) (2 marks): A student suggests that the entropy change for the formation of sodium chloride must be positive as the reaction occurs easily. Is the student correct? Justify
  9. Summer 2022, Unit 3, Q10(e) (3 marks): Some data regarding the dissociation of another weak acid, HX, at two different temperatures are given in the table. H+ X– HX + HX HX at 298 K at temperature T
  10. Summer 2019, Unit 3, Q6 (1 mark): The entropy change of the reaction shown below is positive. Give a reason for this. [1] Na2CO3(aq) + 2HCl(aq) 2NaCl(aq) + CO2(g) + H2O(l)
  11. Summer 2019, Unit 3, Q9(b)(i) (3 marks): A laboratory manual suggests a minimum temperature of 200 °C to remove all the water from the hydrated calcium chloride. At this temperature the reaction occurr
  12. Summer 2018, Unit 3, Q6 (1 mark): The enthalpy of solution of sodium chloride is +4 kJ mol–1. Explain why this compound is soluble 6 in water despite this value being positive. [1]
  13. Summer 2018, Unit 3, Q11(d) (1 mark): State whether you would expect the entropy change for the decomposition of hydrogen peroxide to be positive or negative. Give a reason for your answer. [1]
  14. Summer 2017, Unit 3, Q6 (1 mark): Place the following substances in order of increasing entropy under standard conditions. [1] nitrogen gas copper metal water air Lowest Highest
  15. Summer 2017, Unit 3, Q10(d)(i) (3 marks): [3] ΔGθ = kJ mol−1
  16. Summer 2017, Unit 3, Q10(d)(ii) (1 mark): An alternative method of preparing aqua regia is to use concentrated hydrochloric acid with concentrated nitric acid. State, giving a reason, the effect of this

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