Lesson 13B.1

13B.1 Entropy and the total entropy change Quiz: Pearson Edexcel Chemistry, Unit 13

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 13B.1, Entropy and the total entropy change: 20 multiple choice questions for the Pearson Edexcel Chemistry (9CH0), Unit 13: Energetics II, written with Revision Ninja.

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The 20 questions

  1. What is entropy?

    • A measure of the temperature at which a reaction becomes feasible, found from the ratio of enthalpy and entropy
    • A measure of the total energy stored as chemical bonds in a system, which can be released as heat
    • A measure of the disorder of a system, where a positive entropy change means increased disorder
    • A measure of the mass of reactants used up in a reaction, which determines the theoretical yield

  2. In which direction does a natural, spontaneous change proceed in terms of total entropy?

    • Total entropy stays constant in all natural changes
    • Total entropy is always zero for any chemical reaction
    • Total entropy decreases in every spontaneous change
    • Total entropy increases, giving a positive total entropy change

  3. Which process causes an increase in entropy of the system?

    • A gas condensing to form a liquid
    • Gaseous molecules combining to form a solid
    • A solid melting to form a liquid
    • A liquid freezing to form a solid

  4. Why does N2O4(g) giving 2NO2(g) have a positive entropy change?

    • The number of moles of gas decreases from 2 to 1, so the entropy increases
    • The number of moles of gas stays the same, so the entropy increases
    • The number of moles of gas increases from 1 to 2, so the entropy increases
    • The reaction is exothermic, so the entropy must decrease

  5. Why does dissolving a solid ionic lattice usually increase the entropy of the system?

    • The ions lose kinetic energy and become more ordered in solution as they are held by the solvent
    • The lattice bonds that form between the dissolved ions increase order in the solution overall
    • Water becomes more ordered around the dissolved ions, so the total disorder overall is reduced
    • The ions become free to move and disperse through the solution, increasing disorder

  6. Which expression gives the total entropy change of a reaction?

    • dStotal = dSsystem - dSsurroundings
    • dStotal = dSsystem + dSsurroundings
    • dStotal = dHsystem + dSsurroundings
    • dStotal = dSsystem x dSsurroundings

  7. What are the units of entropy?

    • K mol J-1
    • J K-1 mol-1
    • kJ mol-1
    • J mol-1

  8. Calculate dSsystem for CaCO3(s) gives CaO(s) + CO2(g), using standard entropies of CaCO3 = 93, CaO = 40 and CO2 = 214 J K-1 mol-1. What is the entropy change of the system?

    • +347 J K-1 mol-1
    • +161 J K-1 mol-1
    • -161 J K-1 mol-1
    • -347 J K-1 mol-1

  9. What is the entropy change of the surroundings for a reaction with dH = -92 kJ mol-1 at 298 K?

    • +0.309 J K-1 mol-1
    • +309 J K-1 mol-1
    • +92 J K-1 mol-1
    • -309 J K-1 mol-1

  10. A reaction has dSsystem = -150 J K-1 mol-1 and dH = -92 kJ mol-1 at 298 K. What is dStotal?

    • -241 J K-1 mol-1
    • +459 J K-1 mol-1
    • -159 J K-1 mol-1
    • +159 J K-1 mol-1

  11. Why is the entropy change of the surroundings positive for an exothermic reaction?

    • Heat taken from the surroundings lowers their disorder
    • Exothermic reactions leave the surroundings unchanged
    • Heat released by the reaction increases the disorder of the surroundings
    • Exothermic reactions reduce the temperature of the surroundings, making dSsurroundings negative

  12. Dissolving NH4NO3 is endothermic but happens spontaneously at room temperature. What drives it?

    • A negative entropy change, because the ions lose disorder and become fixed around the water molecules
    • The surroundings lose entropy as the solution cools, so the total entropy change of the process is negative
    • The enthalpy change is zero for an endothermic salt, so no energy is needed from the surroundings
    • A positive entropy change from ions dispersing in solution outweighs the unfavourable enthalpy change

  13. What is the sign of dSsystem for burning magnesium ribbon in air, 2Mg(s) + O2(g) gives 2MgO(s)?

    • Negative, because gas is consumed and a solid forms
    • Positive, because magnesium oxide has a high melting point
    • Positive, because the metal burns with the emission of light
    • Zero, because the solid products balance the reactants

  14. Which process has the most positive entropy change per mole?

    • Liquid to gas, as in vaporisation
    • Aqueous ions to a solid crystal
    • Solid to liquid, as in melting
    • Gas to liquid, as in condensation

  15. Why is the entropy change positive when ethanoic acid reacts with ammonium carbonate to release CO2?

    • The number of gas molecules decreases, so the entropy falls
    • Water is formed, so the entropy of the system falls
    • The reaction is in solution, so the entropy is zero
    • A gas is released, so the number of gas molecules increases

  16. What is dStotal for an exothermic reaction with dH = -92 kJ mol-1, dSsystem = -150 J K-1 mol-1 and T = 500 K?

    • +34 J K-1 mol-1
    • +334 J K-1 mol-1
    • -34 J K-1 mol-1
    • +184 J K-1 mol-1

  17. A student says a reaction with negative dH must be feasible. Which evaluation is best?

    • Correct, because a negative dH always gives a positive entropy change in the system, so the reaction is feasible
    • Incorrect, because enthalpy has no effect on feasibility at any temperature, since only entropy matters
    • Incorrect, because feasibility depends on dStotal, and a large negative dSsystem can make dStotal negative even when dH is negative
    • Correct, because any reaction with negative dH always has a positive dStotal at every temperature

  18. A reaction has dH = +50 kJ mol-1 and dSsystem = +200 J K-1 mol-1. Above what temperature is dStotal positive?

    • Above 250 K, because dStotal = 200 - 50000/T is positive only when T is greater than 250 K
    • Above 500 K, because the enthalpy term must be doubled before the total entropy change turns positive
    • Only at 298 K, because dStotal is exactly zero at room temperature and so the reaction is balanced
    • Above 50 K, because dStotal is positive once the enthalpy change exceeds the entropy change in value

  19. What is dSsurroundings for an endothermic reaction with dH = +50 kJ mol-1 at 298 K?

    • -168 J K-1 mol-1
    • -50 J K-1 mol-1
    • +168 J K-1 mol-1
    • +50 J K-1 mol-1

  20. Why is the total entropy change, rather than the system entropy change alone, the criterion for feasibility?

    • Because the surroundings never change in any reaction, so their entropy can be ignored in the calculation
    • Because system entropy alone always decides spontaneity at every temperature and pressure of the process
    • Because the total entropy change of the system and surroundings must be positive for a process to be spontaneous
    • Because entropy is only defined for the surroundings of a closed system, not for the reacting system itself

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