Lesson 5.2.2

5.2.2 Enthalpy and entropy Quiz: OCR Chemistry, Unit 4

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 5.2.2, Enthalpy and entropy: 20 multiple choice questions for the OCR Chemistry (H432), Unit 4: Physical chemistry and transition elements, written with Revision Ninja.

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The 20 questions

  1. What fundamental property does entropy measure in a system?

    • Total heat content
    • Dispersal of energy
    • Rate of reaction
    • Activation energy

  2. Which of the following has the highest entropy at the same temperature and pressure?

    • Carbon dioxide gas
    • Solid sodium chloride
    • Solid ice
    • Liquid water

  3. What is the sign of the entropy change when the number of gas molecules increases?

    • Negative
    • Unpredictable
    • Positive
    • Zero

  4. Why does entropy increase when a solid ionic compound dissolves in water?

    • Ions form crystals
    • Temperature drops
    • Molecules stop moving
    • Ions become dispersed

  5. Which equation is used to calculate the free energy change of a process?

    • Delta G = Delta H - T Delta S
    • Delta G = T Delta H - Delta S
    • Delta G = Delta H + T Delta S
    • Delta G = Delta S - Delta H / T

  6. What value must Gibbs free energy change have for a process to be feasible?

    • Infinite
    • Positive
    • Negative
    • Zero

  7. For a reaction at 298 K with Delta H = -92 kJ mol^-1 and Delta S = -199 J K^-1 mol^-1, what is Delta G?

    • -33 kJ mol^-1
    • -151 kJ mol^-1
    • +33 kJ mol^-1
    • -92 kJ mol^-1

  8. Calcium carbonate decomposes with Delta H = +178 kJ mol^-1 and Delta S = +161 J K^-1 mol^-1. At what temperature does Delta G become zero, so the decomposition is just feasible?

    • About 1700 K
    • About 1.1 K
    • About 1100 K
    • About 830 K

  9. A reaction has Delta H = +40 kJ mol^-1 and Delta S = +200 J K^-1 mol^-1. Above what temperature is the reaction feasible?

    • 0.2 K
    • 2000 K
    • 200 K
    • 5 K

  10. At which temperatures is a reaction with negative enthalpy and negative entropy changes feasible?

    • Low temperatures
    • High temperatures
    • All temperatures
    • No temperatures

  11. At which temperatures is a reaction with positive enthalpy and positive entropy changes feasible?

    • Low temperatures
    • High temperatures
    • All temperatures
    • No temperatures

  12. Which equation calculates the entropy change of the surroundings?

    • Delta H x T
    • -Delta H / T
    • Delta H / T
    • -T / Delta H

  13. Delta H = -50 kJ mol^-1 and Delta S = -100 J K^-1 mol^-1 for a reaction at 400 K. What is Delta G?

    • -90 kJ mol^-1
    • -50 kJ mol^-1
    • -10 kJ mol^-1
    • +10 kJ mol^-1

  14. If a reaction has negative ΔH and negative ΔS, what happens to ΔG as temperature increases?

    • Remains unchanged
    • Equals zero
    • Becomes positive
    • Becomes negative

  15. Why might a reaction with a negative ΔG fail to occur at room temperature?

    • Endothermic enthalpy change
    • Low activation energy
    • Positive entropy change
    • High activation energy

  16. Which change of state results in a decrease in system entropy?

    • Gas to liquid
    • Liquid to gas
    • Solid to liquid
    • Solid to gas

  17. Using standard entropies in J K^-1 mol^-1 of CaCO3(s) 92.9, CaO(s) 39.8 and CO2(g) 213.8, what is the entropy change for CaCO3 -> CaO + CO2?

    • +53.1 J K^-1 mol^-1
    • -160.7 J K^-1 mol^-1
    • +160.7 J K^-1 mol^-1
    • +346.5 J K^-1 mol^-1

  18. Calculate ΔG at 500 K when ΔH = +50 kJ mol⁻¹ and ΔS = +120 J K⁻¹ mol⁻¹.

    • +10 kJ mol⁻¹
    • -10 kJ mol⁻¹
    • +110 kJ mol⁻¹
    • -59 950 kJ mol⁻¹

  19. How is the entropy change of a system, ΔS, calculated for a chemical reaction?

    • S(reactants) - S(products)
    • S(surroundings) - S(system)
    • S(products) - S(reactants)
    • S(products) + S(reactants)

  20. What happens to the entropy of the system when liquid water freezes into ice?

    • It remains unchanged
    • It becomes zero
    • It increases
    • It decreases

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