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Gibbs free energy Knowledge-Based Practice

Chemistry · Thermochemistry & Thermodynamics · Chemistry · Entropy & Free Energy

5 Chemistry practice questions on Gibbs free energy. Questions that assess core concepts and understanding.

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Questions

  1. 1.

    For a process occurring in a closed system at constant temperature and pressure, what thermodynamic quantity is equal to −ΔG-\Delta G?

    • A) The total enthalpy change of the system during an irreversible expansion
    • B) The total pressure-volume work performed by the expanding reaction mixture
    • C) The net heat exchanged with the surroundings during an endothermic change
    • D) The maximum non-expansion work that the system can perform on its surroundings
  2. 2.

    A chemical reaction has a negative standard Gibbs free energy change (ΔG∘<0\Delta G^\circ < 0) at a temperature of 298 K. What does this indicate about the thermodynamic equilibrium constant, KK, for the reaction at this temperature?

    • A) K<0K < 0
    • B) 0<K<10 < K < 1
    • C) K>1K > 1
    • D) K=1K = 1
  3. 3.

    Under which combination of signs for enthalpy change (ΔH\Delta H) and entropy change (ΔS\Delta S) is a chemical process non-spontaneous at all temperatures?

    • A) ΔH<0\Delta H < 0 and ΔS>0\Delta S > 0
    • B) ΔH<0\Delta H < 0 and ΔS<0\Delta S < 0
    • C) ΔH>0\Delta H > 0 and ΔS<0\Delta S < 0
    • D) ΔH>0\Delta H > 0 and ΔS>0\Delta S > 0
  4. 4.

    A chemical reaction has a standard enthalpy change of ΔH∘=−80.0 kJ⋅mol−1\Delta H^\circ = -80.0\text{ kJ}\cdot\text{mol}^{-1} and a standard entropy change of ΔS∘=−200 J⋅mol−1⋅K−1\Delta S^\circ = -200\text{ J}\cdot\text{mol}^{-1}\cdot\text{K}^{-1}. What is the standard Gibbs free energy change, ΔG∘\Delta G^\circ, at 298 K298\text{ K}, and is the reaction spontaneous under standard conditions at this temperature?

    • A) ΔG∘=−20.4 kJ⋅mol−1\Delta G^\circ = -20.4\text{ kJ}\cdot\text{mol}^{-1}; spontaneous
    • B) ΔG∘=−20.4 kJ⋅mol−1\Delta G^\circ = -20.4\text{ kJ}\cdot\text{mol}^{-1}; non-spontaneous
    • C) ΔG∘=−139.6 kJ⋅mol−1\Delta G^\circ = -139.6\text{ kJ}\cdot\text{mol}^{-1}; spontaneous
    • D) ΔG∘=+20.4 kJ⋅mol−1\Delta G^\circ = +20.4\text{ kJ}\cdot\text{mol}^{-1}; non-spontaneous
  5. 5.

    A chemical reaction has standard thermodynamic values of ΔH∘=+45 kJ⋅mol−1\Delta H^\circ = +45\text{ kJ}\cdot\text{mol}^{-1} and ΔS∘=+125 J⋅mol−1⋅K−1\Delta S^\circ = +125\text{ J}\cdot\text{mol}^{-1}\cdot\text{K}^{-1}. Assuming these values remain constant with temperature, at which temperatures is the reaction spontaneous under standard conditions?

    • A) T>360 KT > 360\text{ K}
    • B) T<360 KT < 360\text{ K}
    • C) T>278 KT > 278\text{ K}
    • D) T<0.36 KT < 0.36\text{ K}

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