The degree of dissociation of `PCl_(5)`

Options

A. Increases with increasing pressure
B. Decreases with increasing pressure
C. No effect on change in pressure
D. Decreases with decreasing pressure

Explanation

To determine the effect of pressure on the degree of dissociation of \( PCl_5 \), we can follow these steps:

### Step-by-Step Solution:

1. **Write the Dissociation Reaction**:
The dissociation of phosphorus pentachloride (\( PCl_5 \)) can be represented by the following equilibrium reaction:
\[ PCl_5 (g) \rightleftharpoons PCl_3 (g) + Cl_2 (g) \]

2. **Identify Moles on Each Side**:
In this reaction, we have:
- Reactants: 1 mole of \( PCl_5 \)
- Products: 1 mole of \( PCl_3 \) + 1 mole of \( Cl_2 \) = 2 moles

3. **Apply Le Chatelier's Principle**:
According to Le Chatelier's principle, if the pressure of a system at equilibrium is increased, the system will shift in the direction that reduces the pressure. This means it will favor the side with fewer moles of gas.

4. **Analyze the Effect of Increasing Pressure**:
Since there is 1 mole of \( PCl_5 \) on the reactant side and 2 moles of products (\( PCl_3 \) and \( Cl_2 \)) on the product side, increasing the pressure will favor the formation of \( PCl_5 \) (the reactant side) because it has fewer moles (1 mole).

5. **Conclusion on Degree of Dissociation**:
As the equilibrium shifts to the left (towards the reactants) when pressure is increased, the degree of dissociation of \( PCl_5 \) will decrease. Therefore, the degree of dissociation of \( PCl_5 \) decreases with increasing pressure.

### Final Answer:
The degree of dissociation of \( PCl_5 \) decreases with increasing pressure.