Question

Given below are two statements:
Statement I: Physical equilibrium takes place only in closed systems at a given temperature
Statement II: For an equilibrium reaction, $\Delta_r G$ is zero

• A. Both statement I and statement II are correct
• B. Both statement I and statement II are not correct
• C. Statement I is correct but statement II is not correct
• D. Statement I is not correct but statement II is correct

Hint:

Do not confuse $\Delta G$ (which is zero at equilibrium) with $\Delta G^\ominus$ (which is only zero when the equilibrium constant $K = 1$).
At any equilibrium, $\Delta G = 0$ is always true.

Answer 1

The Correct Option is A

Step 1: Check statement I on its own terms.
A physical equilibrium such as liquid and vapour coexisting can only be maintained if nothing escapes the system, which is exactly what a closed vessel at fixed temperature guarantees, so this statement holds.
Step 2: Check statement II using thermodynamics.
At any stage of a reaction, $\Delta_rG = \Delta_rG^\ominus + RT\ln Q$. At equilibrium $Q=K$, and since $\Delta_rG^\ominus = -RT\ln K$, substituting gives $\Delta_rG = -RT\ln K + RT\ln K = 0$.
Step 3: Combine both checks.
Both statements independently hold up under scrutiny.
Final answer: Option 1, both statement I and statement II are correct.