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Question

Difficulty: MediumEntropy, Free Energy and Reaction Spontaneity

Match each thermodynamic state or free energy parameter on the left with its correct spontaneity or equilibrium interpretation on the right.

  • ΔG=0\Delta G = 0The reaction system is at dynamic equilibrium with no net driving force in either direction.
  • ΔG<0\Delta G < 0The reaction proceeds spontaneously in the forward direction under the given conditions.
  • ΔG>0\Delta G > 0The reaction is non-spontaneous in the forward direction, and the reverse reaction is thermodynamically favored.
  • ΔG∘<0\Delta G^\circ < 0Products are thermodynamically favored over reactants at equilibrium under standard conditions (Keq>1K_{eq} > 1).

Answer

The correct matches pair ΔG=0\Delta G = 0 with dynamic equilibrium, ΔG<0\Delta G < 0 with spontaneous forward reaction, ΔG>0\Delta G > 0 with non-spontaneous forward reaction, and ΔG∘<0\Delta G^\circ < 0 with product favorability at standard equilibrium (Keq>1K_{eq} > 1).
The correct matches pair each thermodynamic free energy symbol with its fundamental definition: ΔG=0\Delta G = 0 represents dynamic equilibrium, ΔG<0\Delta G < 0 represents a spontaneous forward process, ΔG>0\Delta G > 0 represents a non-spontaneous forward process, and ΔG∘<0\Delta G^\circ < 0 represents standard product favorability (Keq>1K_{eq} > 1).

Step-by-Step Solution

1
Analyze the physical meaning of ΔG=0\Delta G = 0.
ΔG=0\Delta G = 0 corresponds to a state of dynamic equilibrium where the rate of the forward reaction equals the rate of the reverse reaction.
At equilibrium, there is no net change in free energy.
2
Analyze the condition for spontaneity (ΔG<0\Delta G < 0).
ΔG<0\Delta G < 0 indicates an exergonic, spontaneous forward reaction under the specified conditions.
Thermodynamics dictates that spontaneous processes decrease free energy to reach stability.
3
Analyze non-spontaneous conditions (ΔG>0\Delta G > 0).
ΔG>0\Delta G > 0 means energy input is required for the forward reaction, making the reverse reaction spontaneous.
A positive free energy change signifies an endergonic process.
4
Evaluate standard free energy ΔG∘<0\Delta G^\circ < 0 in relation to the equilibrium constant.
Using ΔG∘=−RTln⁡Keq\Delta G^\circ = -RT \ln K_{eq}, a negative ΔG∘\Delta G^\circ implies ln⁡Keq>0\ln K_{eq} > 0, so Keq>1K_{eq} > 1.
When Keq>1K_{eq} > 1, products are favored over reactants at standard equilibrium.

Key Concept

Gibbs Free Energy and Reaction Spontaneity Criteria
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Topics

Entropy, Free Energy and Reaction Spontaneity