13B.3 Free energy, feasibility and equilibrium Quiz: Pearson Edexcel Chemistry, Unit 13

The 20 questions

1. Which equation correctly defines the Gibbs free energy change, ΔG?

   • ΔG = ΔH / TΔS
   • ΔG = ΔH + TΔS
   • ΔG = TΔS - ΔH
   • ΔG = ΔH - TΔS

2. What value of ΔG indicates that a chemical reaction is thermodynamically feasible?

   • ΔG ≤ 0
   • ΔG > 0
   • ΔG = +1
   • ΔG > ΔH

3. What does a large equilibrium constant (K >> 1) indicate about ΔG?

   • ΔG is zero
   • ΔG equals ΔH
   • ΔG is negative
   • ΔG is positive

4. At what temperature is a reaction at equilibrium, with dG = 0?

   • T = dS / dH
   • T = dH / dS
   • T = dH x dS
   • T = dG / dH

5. Which condition allows an endothermic reaction to be feasible at room temperature?

   • Low temperature
   • Large positive ΔS
   • Large negative ΔH
   • Large negative ΔS

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

   • Positive ΔS
   • High activation energy
   • Low activation energy
   • Exothermic enthalpy change

7. In ΔG = ΔH - TΔS, how is ΔS in J K-1 mol-1 converted to kJ K-1 mol-1?

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

8. For dH = +180 kJ mol-1 and dS = +160 J K-1 mol-1, at what temperature does dG become zero?

   • 340 K
   • 0.889 K
   • 1125 K
   • 28800 K

9. For ΔH = -92 kJ mol-1 and ΔS = -198 J K-1 mol-1 at 298 K, what is ΔG?

   • +58.9 kJ mol-1
   • -33.0 kJ mol-1
   • +33.0 kJ mol-1
   • -151.0 kJ mol-1

10. For ΔH = +50 kJ mol-1 and ΔS = +100 J K-1 mol-1 at 298 K, what is ΔG?

    • -20.2 kJ mol-1
    • +20.2 kJ mol-1
    • +79.8 kJ mol-1
    • -29.8 kJ mol-1

11. For ΔH = +50 kJ mol-1 and ΔS = +100 J K-1 mol-1, above what temperature is the reaction feasible?

    • 250 K
    • 298 K
    • 500 K
    • 0.5 K

12. For dG = -10 kJ mol-1 at 298 K, what is the equilibrium constant K approximately?

    • About 2.5 x 10^3
    • About 57
    • About 0.018
    • About 4.0

13. For dG = +5 kJ mol-1 at 298 K, what is K approximately?

    • About 0.13
    • About 0.0067
    • About 1.0
    • About 7.5

14. When both ΔH and ΔS are negative, at what temperatures is the reaction feasible?

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

15. What is ΔG at 500 K if ΔH = -92 kJ mol⁻¹ and ΔS = -198 J K⁻¹ mol⁻¹?

    • -191 kJ mol⁻¹
    • +191 kJ mol⁻¹
    • +7.0 kJ mol⁻¹
    • -7.0 kJ mol⁻¹

16. For dH = -92 kJ mol-1 and dS = -198 J K-1 mol-1, what is the temperature at which dG = 0?

    • About 0.46 K
    • About 2150 K
    • About 465 K
    • About 298 K

17. Why might a thermodynamically feasible reaction with a negative ΔG fail to occur rapidly?

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

18. What is ΔG at 298 K for a reaction with equilibrium constant K = 1.0 × 10⁵?

    • +28.5 kJ mol⁻¹
    • -12.4 kJ mol⁻¹
    • +12.4 kJ mol⁻¹
    • -28.5 kJ mol⁻¹

19. What is the value of the equilibrium constant K when ΔG equals zero?

    • -1
    • Infinity
    • 1
    • 0

20. What combination of enthalpy and entropy changes makes a reaction feasible only at high temperatures?

    • Negative ΔH, negative ΔS
    • Positive ΔH, negative ΔS
    • Positive ΔH, positive ΔS
    • Negative ΔH, positive ΔS

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