7.7 Gibbs Free Energy Change and Feasibility of a Reaction

This topic explains how Gibbs free energy change determines whether a reaction is feasible. It describes the conditions for feasibility and connects to the concept of spontaneity.

Definition

Feasible Reaction: A reaction that will go to completion, without any energy being supplied to it.

Gibbs Free Energy Change (ΔG): A measure used to predict whether a reaction is feasible.

Main Idea

Free energy change, ΔG, is a measure to predict whether a reaction is feasible. A feasible reaction is one which will go to completion, without any energy being supplied to it. If ΔG is negative or equal to zero, then the reaction is feasible. If ΔG° is positive, then the reaction is not feasible.

Core Concept

Detailed Explanation

What is a Feasible Reaction?

• A feasible reaction is one which will go to completion, without any energy being supplied to it.
• Free energy change, ΔG, is a measure to predict whether a reaction is feasible.

Conditions for Feasibility

• If ΔG is negative or equal to zero, then the reaction is feasible.
• If ΔG° is positive, then the reaction is not feasible.

Connection to Previous Concepts

For more information, see section 6.7 (Gibbs Free Energy).

In section 6.7, we learned: Δ G^° = Δ H^° - TΔ S^°

• ΔG° < 0: Spontaneous in forward direction.
• ΔG° > 0: Non-spontaneous in forward direction.
• **ΔG° = 0:** System at equilibrium.

Summary

• **Feasible:** ΔG < 0 or ΔG = 0
• Not feasible: ΔG > 0

Intermediate Level

Feasibility of a Reaction

Formula

Δ G^° = Δ H^° - TΔ S^°

• ΔG° < 0: Spontaneous
• ΔG° > 0: Non-spontaneous
• ΔG° = 0: Equilibrium

Key Point

• A feasible reaction goes to completion without external energy.
• ΔG determines feasibility.

Important Points

• 1. Feasible reaction: Goes to completion without energy.
• 2. ΔG < 0: Feasible.
• 3. ΔG = 0: Equilibrium.
• 4. ΔG > 0: Not feasible.
• 5. ΔG° = ΔH° − TΔS°.
• 6. See section 6.7 for more information.

Remember

• - ΔG < 0: Feasible
• - **ΔG = 0:** Equilibrium
• - ΔG > 0: Not feasible
• - **Formula:** ΔG° = ΔH° − TΔS°

Common Mistakes

• 1. Confusing feasible with spontaneous: Feasible means it can occur; spontaneous means it occurs without external energy.
• 2. Forgetting the sign of ΔG: Negative = feasible; Positive = not feasible.
• 3. Mixing up ΔG and ΔH: ΔG includes both enthalpy and entropy.
• 4. Thinking ΔG > 0 means reaction never happens: It means non-spontaneous, but can be driven by external energy.

Quick Revision

• Feasible reaction: Goes to completion without energy.
• ΔG < 0: Feasible.
• ΔG = 0: Equilibrium.
• ΔG > 0: Not feasible.
• ΔG° = ΔH° − TΔS°.
• See section 6.7 for more information.

60-Second Revision

• ΔG < 0: Feasible
• **ΔG = 0:** Equilibrium
• ΔG > 0: Not feasible
• **Formula:** ΔG° = ΔH° − TΔS°

QUALITY VALIDATION

• Topic: 7.7 Gibbs Free Energy Change and Feasibility of a Reaction
• Chapter: 7 (Chemical Kinetics)

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