Question

Identify the reaction in which entropy change is positive ($\Delta S>0$).

• A. $2\text{H}_2\text{O}_{2(\text{l})} \to 2\text{H}_2\text{O}_{(\text{l})} + \text{O}_{2(\text{g})}$
• B. $\text{NH}_{3(\text{g})} + \text{HCl}_{(\text{g})} \to \text{NH}_4\text{Cl}_{(\text{s})}$
• C. $\text{H}_{2(\text{g})} + \text{Cl}_{2(\text{g})} \to 2\text{HCl}_{(\text{g})}$
• D. $\text{N}_{2(\text{g})} + 3\text{H}_{2(\text{g})} \to 2\text{NH}_{3(\text{g})}$

Hint:

Look for reactions where the total number of gaseous moles on the product side is greater than on the reactant side.

Answer 1

The Correct Option is A

Step 1: Concept
$\Delta S>0$ when disorder increases. This typically happens when: - Number of gaseous moles increases. - Phase changes from solid $\to$ liquid $\to$ gas.
Step 2: Analysis
- (A) Liquid reactant $\to$ Liquid + Gas product. Moles of gas increase ($0 \to 1$). $\Delta S>0$. - (B) Gas + Gas $\to$ Solid. Moles of gas decrease. $\Delta S<0$. - (C) $2$ moles gas $\to 2$ moles gas. $\Delta S \approx 0$. - (D) $4$ moles gas $\to 2$ moles gas. $\Delta S<0$.
Final Answer: (A)