Question

Which one of the following is the CORRECT representation of the variation of the Gibbs free energy (( G )) of a substance with temperature (( T )) at constant pressure?

• A.
• B.
• C.
• D.

Hint:

For thermodynamic stability, the phase with the lowest Gibbs free energy (( G )) at a specific temperature is the most stable. Phase transitions occur where the ( G ) lines of two phases intersect.

Answer 1

The Correct Option is A

Step 1: Understanding Gibbs free energy (\( G \)) dependence on temperature.

Gibbs free energy (\( G \)) is a thermodynamic potential that decreases as the temperature (\( T \)) increases for a given phase. The phase with the lowest \( G \) at a particular \( T \) is the stable phase.

Step 2: Behavior of \( G \) for different phases.

• Solids have the lowest entropy and the most stable \( G \) at low \( T \).
• Liquids have moderate entropy and become stable at intermediate \( T \).
• Gases have the highest entropy and are stable at high \( T \).

Step 3: Analyzing the diagrams.

Option (A) correctly depicts the sequence:

\[ G_{\text{solid}} > G_{\text{liquid}} > G_{\text{gas}} \]

at increasing temperatures (\( T \)) with intersecting lines at phase transition points.