Suppose the reaction `PC1_(5(s))hArrPC1_(3(s)) + C1_(2(g))` is in a closed vessel at equilibrium stage. What is the effect on equilibrium concentration of `C1_(2(g))` by adding `PCl_(5)` at constant temperature ?

Options

A. Unaffected
B. Increases
C. Decreases
D. Cannot be described without the value of `K_p`

Answer

To solve the question regarding the effect on the equilibrium concentration of \( Cl_2(g) \) when \( PCl_5(s) \) is added at constant temperature, we can follow these steps:

### Step 1: Understand the Reaction
The equilibrium reaction given is:
\[ PCl_5(s) \rightleftharpoons PCl_3(s) + Cl_2(g) \]

### Step 2: Identify the Components
- \( PCl_5 \) is a solid and does not affect the equilibrium concentration in terms of pressure or concentration since solids do not appear in the equilibrium expression.
- \( PCl_3 \) is also a solid and similarly does not affect the equilibrium.
- \( Cl_2 \) is a gas and its concentration will be affected by changes in the equilibrium.

### Step 3: Apply Le Chatelier's Principle
According to Le Chatelier's Principle, if a system at equilibrium is disturbed, the system will adjust to counteract the disturbance and restore a new equilibrium.

### Step 4: Analyze the Effect of Adding \( PCl_5 \)
When \( PCl_5 \) is added to the system:
- The concentration of \( PCl_5 \) increases.
- Since \( PCl_5 \) is a solid, its addition does not change the concentration in terms of the equilibrium expression.
- However, the system will respond by shifting the equilibrium to the right to consume some of the \( PCl_5 \) and produce more \( Cl_2 \).

### Step 5: Conclusion on \( Cl_2(g) \) Concentration
As a result of the shift to the right, the concentration of \( Cl_2(g) \) will increase.

### Final Answer
The equilibrium concentration of \( Cl_2(g) \) will **increase** upon adding \( PCl_5 \) at constant temperature.

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