JEE Chemistry 2025 Question with Solution

Given: The system changes from solution 1 to solution 2. Both solutions have the same composition, namely $1$ mole of $x$ in $1 \, \text{L}$ of $H_2O$.

Find: Which property changes during this transition.

Use the distinction between intensive and extensive properties.

• Intensive properties do not depend on the amount of substance.
• Extensive properties depend on the total amount of substance.

Since both solutions have the same composition, intensive properties such as molar heat capacity, density, and concentration remain the same.

However, the total amount of the system is different in solution 1 and solution 2. Therefore, an extensive thermodynamic property will change.

Gibbs free energy $G$ is an extensive property, so it will be different for the two systems.

Therefore, the correct option is D.

Given: Solution 1 contains a larger total amount than solution 2, but both have the same composition.

Find: The property that changes when moving from solution 1 to solution 2.

Approach the options one by one:

1. Molar heat capacity is defined per mole, so it is an intensive property.
2. Density depends on mass per unit volume and, for the same composition, remains unchanged.
3. Concentration is the amount of solute per unit volume, and since the composition is the same, it remains unchanged.
4. Gibbs free energy $G$ changes with the state and total amount of the system, so it is different for the two solutions.

Because the concentration is unchanged but the total amount is different, the extensive property Gibbs free energy changes.

Hence, the correct answer is D.