For the reaction `PCl_(5)(g)hArrPCl_(3)(g)+Cl_(2)(g)` the forward reaction at constant temperature is favoured by

Options

A. Introducing an inert gas at constant volume
B. Introducing `PCl_(3)(g)` gas at constnt volume
C. Introducing `PCl_(5)(g)` gas at constant volume
D. Introducing `Cl_(2)(g)` gas at constant volume

Answer

To determine which action will favor the forward reaction for the equilibrium:

\[ \text{PCl}_5(g) \rightleftharpoons \text{PCl}_3(g) + \text{Cl}_2(g) \]

we can apply Le Chatelier's principle, which states that if a system at equilibrium is subjected to a change in concentration, pressure, or temperature, the system will adjust to counteract that change and restore a new equilibrium.

### Step-by-Step Solution:

1. **Identify the Reaction Components**:
The reaction involves one reactant (PCl5) and two products (PCl3 and Cl2).

2. **Understand Le Chatelier's Principle**:
According to this principle, if we increase the concentration of a reactant, the equilibrium will shift to the right (forward direction) to produce more products. Conversely, if we increase the concentration of a product, the equilibrium will shift to the left (backward direction).

3. **Analyze Each Option**:
- **Option A**: Introducing an inert gas at constant volume.
- Inert gases do not react with the components of the equilibrium and do not change the partial pressures of the reactants or products. Therefore, this will have no effect on the equilibrium position.
- **Option B**: Introducing PCl3 gas at constant volume.
- Increasing the concentration of PCl3 (a product) will shift the equilibrium to the left (backward direction), which is not favorable for the forward reaction.
- **Option C**: Introducing PCl5 gas at constant volume.
- Increasing the concentration of PCl5 (a reactant) will shift the equilibrium to the right (forward direction), which favors the formation of products.
- **Option D**: Introducing Cl2 gas at constant volume.
- Increasing the concentration of Cl2 (a product) will also shift the equilibrium to the left (backward direction), which is not favorable for the forward reaction.

4. **Conclusion**:
The only action that favors the forward reaction is **Option C: introducing PCl5 gas at constant volume**. This will increase the concentration of the reactant, thereby shifting the equilibrium to the right.

### Final Answer:
**Option C: Introducing PCl5 gas at constant volume.**

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