For which of the following processes, entropy change is negative?

Options

A. Evaporation of water
B. Sublimation of camphor
C. Condensation of iodine vapour
D. Melting of ice

Answer

To determine for which of the given processes the entropy change is negative, we need to analyze each process based on the concept of entropy. Entropy is a measure of the disorder or randomness of a system, and it generally increases when a system goes from a more ordered state to a less ordered state.

### Step-by-Step Solution:

1. **Understand Entropy**:
- Entropy (S) is a measure of the randomness or disorder of a system.
- An increase in entropy indicates a transition to a more disordered state, while a decrease indicates a transition to a more ordered state.

2. **Evaluate Each Process**:
- **Option 1: Evaporation of Water (H2O liquid → H2O gas)**:
- In this process, water transitions from a liquid state (more ordered) to a gaseous state (less ordered).
- Since gas particles have more freedom of movement, the entropy increases.
- **Entropy Change**: Positive.

- **Option 2: Sublimation of CH4 (solid CH4 → gaseous CH4)**:
- Here, methane transitions from a solid state (more ordered) to a gaseous state (less ordered).
- Similar to the previous case, the gaseous state has more freedom of movement, leading to an increase in entropy.
- **Entropy Change**: Positive.

- **Option 3: Condensation of Iodine Vapour (I2 gas → I2 liquid)**:
- In this process, iodine transitions from a gaseous state (more disordered) to a liquid state (more ordered).
- The gaseous state has more freedom of movement compared to the liquid state, indicating a decrease in entropy.
- **Entropy Change**: Negative.

- **Option 4: Melting of Ice (solid H2O → liquid H2O)**:
- Here, ice (solid) transitions to water (liquid).
- The transition from solid to liquid represents an increase in disorder as the particles in the liquid state can move more freely than in the solid state.
- **Entropy Change**: Positive.

3. **Conclusion**:
- After evaluating all options, the only process that results in a negative change in entropy is the condensation of iodine vapour (Option 3).

### Final Answer:
The process for which the entropy change is negative is **Option 3: Condensation of Iodine Vapour**.

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