Ammonium chloride when dissolved in water leads to a cooling sensation. The dissolution of ammonium chloride at constant temperature is accompanied by

Options

A. Increase in entropy
B. Decrease in entropy
C. No change in entropy
D. No change in enthalpy

Explanation

To solve the question regarding the dissolution of ammonium chloride in water, we will analyze the process step by step.

### Step-by-Step Solution:

1. **Understanding the Dissolution Process**:
- When ammonium chloride (NH4Cl) is added to water, it dissociates into ammonium ions (NH4⁺) and chloride ions (Cl⁻).
- The reaction can be represented as:
\[ \text{NH}_4\text{Cl (s)} + \text{H}_2\text{O (l)} \rightarrow \text{NH}_4^+ \text{(aq)} + \text{Cl}^- \text{(aq)} \]

2. **Observing the Cooling Sensation**:
- The cooling sensation experienced during the dissolution indicates that the process absorbs heat from the surroundings. This suggests that the dissolution is an endothermic process.

3. **Analyzing the Enthalpy Change (ΔH)**:
- The enthalpy change (ΔH) for the dissolution of ammonium chloride is given as +15.1 kJ. A positive ΔH indicates that heat is absorbed during the reaction, confirming that it is endothermic.

4. **Entropy Change (ΔS)**:
- Entropy is a measure of disorder or randomness in a system. In this case, we are moving from a solid state (NH4Cl) to a more disordered state (aqueous ions NH4⁺ and Cl⁻).
- The increase in the number of particles and the transition from solid to aqueous form leads to an increase in randomness.

5. **Conclusion**:
- Since the dissolution of ammonium chloride results in an increase in disorder (randomness) and is accompanied by a positive enthalpy change (endothermic), we conclude that the dissolution process is accompanied by an increase in entropy (ΔS > 0).

### Final Answer:
The dissolution of ammonium chloride in water is accompanied by an **increase in entropy**.

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