Which of the following reactions represents `Delta H` (hydration) :-

Options

A. `CuSO_(4)(s)+(aq)rarr CuSO_(4)(aq) , Delta H=- x KJ`
B. `BaCl_(2)(s)+2H_(2)O(l)rarr BaCl_(2). 2H_(2)O(s) , Delta H=-x' KJ`
C. `CuSO_(4)(s)+5H_(2)O(l)+(aq)rarr CuSO_(4). 5H_(2)O(aq) , Delta H =-y' KJ`
D. None of the above

Answer

To determine which reaction represents the enthalpy of hydration (ΔH hydration), we need to understand what hydration means in the context of thermodynamics. Hydration refers to the process where ions are surrounded by water molecules, and this process involves the release of energy, which is quantified as the enthalpy change (ΔH).

### Step-by-Step Solution:

1. **Understand Hydration**:
- Hydration occurs when an ionic compound dissolves in water, and the ions become surrounded by water molecules. The water molecules orient themselves around the ions due to their polar nature, with the oxygen atom being partially negative and the hydrogen atoms being partially positive.

2. **Identify the Reaction**:
- We need to look for a reaction that shows an ionic compound dissolving in water, resulting in the formation of hydrated ions. This can be represented as:
\[ \text{Na}^+ (s) + \text{Cl}^- (s) + \text{H}_2\text{O} \rightarrow \text{Na}^+ (aq) + \text{Cl}^- (aq) \]
- In this reaction, solid sodium chloride (NaCl) dissociates into sodium ions (Na⁺) and chloride ions (Cl⁻) in the aqueous phase, surrounded by water molecules.

3. **Energy Change**:
- The process of hydration is exothermic, meaning it releases energy. This energy release is what we refer to as ΔH hydration. The enthalpy change can be represented as:
\[ \Delta H_{\text{hydration}} < 0 \]
- This indicates that energy is released when the ions are hydrated.

4. **Select the Correct Option**:
- Based on the understanding of hydration and the representation of the reaction, we can conclude that the correct option that represents ΔH (hydration) is the one that shows the dissociation of an ionic compound in water, leading to the formation of hydrated ions.

### Conclusion:
The reaction that represents ΔH (hydration) is the one where an ionic compound dissociates in water to form hydrated ions.