`NH_(4)CI(s) + aq rarr NH_(4)^(+)(aq) + CI^(-1)(aq)`
`DeltaH=+15.1 KJ mol^(-1) NH_(4)CI(s)` dissolves in water according to above equation

Options

A. Dissolution of `NH_(4) CI(s)` in water in a spontaneous reverssible process
B. Gibbs free energy and entropy both are negative.
C. Above process is reverssible in which driving force for dissolution is increasing in entropy
D. `DeltaG, DeltaH` and `DeltaS` all are positive.

Answer

To solve the problem regarding the dissolution of NH₄Cl(s) in water, we will analyze the given reaction and the thermodynamic parameters involved.

**Step 1: Understand the reaction**
The dissolution of ammonium chloride (NH₄Cl) in water can be represented as:
\[ \text{NH}_4\text{Cl}(s) \rightarrow \text{NH}_4^+(aq) + \text{Cl}^-(aq) \]
This reaction shows that solid NH₄Cl dissociates into ammonium ions (NH₄⁺) and chloride ions (Cl⁻) in an aqueous solution.

**Step 2: Analyze the enthalpy change (ΔH)**
The given ΔH for the reaction is +15.1 kJ/mol. This indicates that the dissolution process is endothermic, meaning that it absorbs heat from the surroundings.

**Step 3: Consider the entropy change (ΔS)**
When NH₄Cl dissolves, it goes from a solid state (which has a more ordered structure) to ions in solution (which are more disordered). This typically results in an increase in entropy (ΔS > 0) because the number of microstates available to the system increases.

**Step 4: Apply Gibbs Free Energy (ΔG)**
The relationship between Gibbs free energy, enthalpy, and entropy is given by the equation:
\[ \Delta G = \Delta H - T \Delta S \]
For a process to be spontaneous, ΔG must be negative. Since ΔH is positive (endothermic), the term \( -T \Delta S \) must be sufficiently negative (i.e., ΔS must be positive and large enough) to make ΔG negative.

**Step 5: Evaluate the options**
1. **Option 1:** Dissolution of NH₄Cl solid in water is a spontaneous reversible process.
- This is true because the process is spontaneous at certain temperatures due to the increase in entropy.

2. **Option 2:** Gibbs free energy and entropy both are negative.
- This is false. While ΔG can be negative, ΔH is positive (endothermic), and ΔS is positive (increase in disorder).

3. **Option 3:** The above process is reversible in which the driving force for dissolution is increasing in entropy.
- This is true. The driving force for the dissolution is indeed the increase in entropy.

4. **Option 4:** ΔG, ΔH, and ΔS all are positive.
- This is false. ΔH is positive, but ΔS is positive as well, and ΔG can be negative under the right conditions.

**Conclusion:**
The correct option is **Option 3**, as it correctly describes the process as reversible and identifies the increase in entropy as the driving force for dissolution.

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