13B.2 Calculating entropy changes Quiz: Pearson Edexcel Chemistry, Unit 13

The 20 questions

1. How is the standard entropy change of a system calculated?

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

2. Which factor has the largest effect on the magnitude of a substance's standard entropy?

   • Chemical formula
   • Physical state
   • Molar mass
   • Bond enthalpy

3. What is the entropy value of a perfect crystal at absolute zero?

   • 0 J K⁻¹ mol⁻¹
   • -273 J K⁻¹ mol⁻¹
   • 100 J K⁻¹ mol⁻¹
   • 298 J K⁻¹ mol⁻¹

4. Why do gases have significantly higher standard entropies than liquids?

   • Higher particle density
   • Stronger intermolecular forces
   • Greater particle freedom
   • Fixed particle positions

5. What does a negative entropy change of a system indicate?

   • Unchanged order
   • Increased enthalpy
   • Increased disorder
   • Increased order

6. Which substance has the highest standard entropy at 298 K?

   • Diamond(s)
   • H2O(l)
   • All are equal
   • CO2(g)

7. What sign is the standard entropy of a pure element at 298 K?

   • Negative
   • Positive
   • Variable
   • Zero

8. For N2(g) + 3H2(g) gives 2NH3(g), with S(N2) = 191.5, S(H2) = 130.7 and S(NH3) = 192.8 J K-1 mol-1, what is dS for the system?

   • -198.0 J K-1 mol-1
   • +775.2 J K-1 mol-1
   • -391.2 J K-1 mol-1
   • +198.0 J K-1 mol-1

9. For CaCO3(s) gives CaO(s) + CO2(g), with S(CaCO3) = 92.9, S(CaO) = 39.8 and S(CO2) = 213.8 J K-1 mol-1, what is dS for the system?

   • +266.9 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

10. For 2Mg(s) + O2(g) gives 2MgO(s), with S(Mg) = 32.7, S(O2) = 205.2 and S(MgO) = 26.9 J K-1 mol-1, what is dS for the system?

    • -216.8 J K-1 mol-1
    • +270.6 J K-1 mol-1
    • -54.5 J K-1 mol-1
    • +216.8 J K-1 mol-1

11. For H2O(l) gives H2O(g), with S(l) = 70.0 and S(g) = 188.8 J K-1 mol-1, what is dS for the system?

    • -118.8 J K-1 mol-1
    • +258.8 J K-1 mol-1
    • +118.8 J K-1 mol-1
    • +70.0 J K-1 mol-1

12. For N2O4(g) gives 2NO2(g), with S(N2O4) = 304.3 and S(NO2) = 240.0 J K-1 mol-1, what is dS for the system?

    • +544.3 J K-1 mol-1
    • +175.7 J K-1 mol-1
    • +64.3 J K-1 mol-1
    • -175.7 J K-1 mol-1

13. For CH4(g) + 2O2(g) gives CO2(g) + 2H2O(l), with S(CH4) = 186.3, S(O2) = 205.2, S(CO2) = 213.8 and S(H2O, l) = 69.9 J K-1 mol-1, what is dS for the system?

    • +596.7 J K-1 mol-1
    • -43.1 J K-1 mol-1
    • +243.1 J K-1 mol-1
    • -243.1 J K-1 mol-1

14. For a combustion reaction with dH = -890 kJ mol-1 at 298 K, what is the entropy change of the surroundings?

    • +890 J K-1 mol-1
    • +2.99 J K-1 mol-1
    • +2987 J K-1 mol-1
    • -2987 J K-1 mol-1

15. Convert dS = -243.1 J K-1 mol-1 into kJ K-1 mol-1.

    • -2.431 kJ K-1 mol-1
    • -24.31 kJ K-1 mol-1
    • -0.2431 kJ K-1 mol-1
    • -0.02431 kJ K-1 mol-1

16. For a reaction with dS(system) = -243.1 J K-1 mol-1, dH = -890 kJ mol-1 and T = 298 K, what is dStotal?

    • +2743.5 J K-1 mol-1
    • -3229.7 J K-1 mol-1
    • +3229.7 J K-1 mol-1
    • -2743.5 J K-1 mol-1

17. Which entropy change determines whether a chemical reaction is spontaneous?

    • System entropy change
    • Enthalpy change
    • Surroundings entropy change
    • Total entropy change

18. A reaction has dSsystem = -240 J K-1 mol-1 and dH = -120 kJ mol-1. At what temperature is dStotal equal to zero?

    • 500 K
    • 250 K
    • 50 K
    • 2 K

19. For ΔSsystem = +100 J K-1 mol-1 and ΔH = +30 kJ mol-1 at 298 K, what is ΔStotal?

    • +0.7 J K-1 mol-1
    • -0.7 J K-1 mol-1
    • +199.3 J K-1 mol-1
    • -0.1 J K-1 mol-1

20. When calculating ΔStotal, what unit conversion must be applied to ΔH in kJ mol-1?

    • Multiply by 1000
    • Multiply by 298
    • Divide by 298
    • Divide by 1000

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