Question

Identify the correct statements from the following
\[ \text{I. At }0\,K,\text{ the entropy of pure crystalline materials approaches zero.} \] \[ \text{II. Entropy for the process }H_2O(l)\longrightarrow H_2O(g)\text{ decreases.} \] III. Gibbs energy is a state function.

• A. i, ii, iii
• B. i, iii Only
• C. ii, iii Only
• D. i, ii Only

Hint:

Entropy increases when a substance changes from solid \(\rightarrow\) liquid \(\rightarrow\) gas because molecular randomness increases in that order.

Answer 1

The Correct Option is B

Step 1: Evaluate statement I - Third Law of Thermodynamics.
The Third Law states: entropy of a perfectly crystalline substance approaches zero as temperature approaches 0 K. For pure crystalline materials: $S \to 0$ as $T \to 0$ K. Statement I is CORRECT.
Step 2: Evaluate statement II - Entropy for $H_2O(l) \to H_2O(g)$.
Gas molecules have much greater disorder than liquid molecules. Entropy INCREASES when liquid water converts to steam. Statement II says entropy decreases, which is WRONG. Statement II is INCORRECT.
Step 3: Evaluate statement III - Gibbs energy as a state function.
$G = H - TS$. Both $H$ and $S$ are state functions; $T$ is a state variable. A function of state functions is itself a state function. So $G$ is a state function. Statement III is CORRECT.
Step 4: Identify the correct combination of statements.
Statements I and III are correct; Statement II is incorrect. This matches option (2): i and iii only.
Step 5: Confirm the error in statement II.
By Trouton's rule, $\Delta S_{vap} \approx +88$ J/mol/K for most liquids. Entropy always increases during vaporization. Statement II is definitively wrong.
Step 6: State the final answer.
\[ \boxed{\text{I and III only}} \]