Question

Observe the following processes:
I. \( O_2(l) \rightarrow O_2(g) \)
II. \( N_2(g) + 3H_2(g) \rightarrow 2NH_3(g) \)
III. \( C(s, {graphite}) \rightarrow C(s, {diamond}) \)
IV. \( N_2(g, 1 \, {atm}) \rightarrow N_2(g, 10 \, {atm}) \)
V. \( H_2(g) \rightarrow 2H(g) \)
VI. Temperature of a crystalline solid is raised from 0 K to 115 K
For how many of the above processes, change in entropy is negative?

• A. 2
• B. 3
• C. 4
• D. 1

Hint:

Entropy generally increases with temperature, phase transitions to less ordered states, and increases in the number of gas molecules.

Answer 1

The Correct Option is B

Step 1: Analyze each process for entropy change

• \( O_2(l) \rightarrow O_2(g) \): Entropy increases as gas has more disorder than liquid.
• \( N_2(g) + 3H_2(g) \rightarrow 2NH_3(g) \): Entropy decreases as the number of gas molecules decreases.
• \( C(s, \text{graphite}) \rightarrow C(s, \text{diamond}) \): Entropy decreases as diamond is more ordered than graphite.
• \( N_2(g, 1 \text{ atm}) \rightarrow N_2(g, 10 \text{ atm}) \): Entropy decreases as pressure increases, reducing volume and disorder.
• \( H_2(g) \rightarrow 2H(g) \): Entropy increases as the number of gas molecules increases.
• Temperature of a crystalline solid is raised from 0 K to 115 K: Entropy increases as temperature increases, increasing molecular motion.

Step 2: Count the processes with negative entropy change

Processes II, III, and IV have negative entropy changes.

Final Answer: 3