What will be the effect of addition of catalyst at constant temperature ?

Options

A. The equilibrium constant will remain constant
B. `DeltaH` of the reaction will remain constant
C. `K_(f)` and `K_(b)` wil increase upto same extent
D. equilibrium composition will change

Answer

To answer the question regarding the effect of the addition of a catalyst at constant temperature, let's break it down step by step.

### Step-by-Step Solution:

1. **Understanding Catalysts**: A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the process. It does this by lowering the activation energy required for the reaction to occur.

2. **Effect on Reaction Rates**: When a catalyst is added, it increases the rate of both the forward and reverse reactions equally. This means that the catalyst speeds up the attainment of equilibrium but does not change the position of equilibrium itself.

3. **Equilibrium Constant (Kc)**: The equilibrium constant (Kc) is defined as the ratio of the rate of the forward reaction (Kf) to the rate of the backward reaction (Kb). Since a catalyst increases both Kf and Kb to the same extent, the ratio Kc remains constant. Therefore, the equilibrium constant does not change with the addition of a catalyst.

4. **Change in Enthalpy (ΔH)**: The enthalpy change (ΔH) of a reaction is a measure of the heat absorbed or released during the reaction. The addition of a catalyst does not affect the enthalpy change of the reaction; it remains constant.

5. **Effect on Kf and Kb**: As mentioned earlier, both Kf and Kb will increase, but they do so to the same extent. This means that although the rates of the forward and backward reactions increase, their ratio (Kc) remains unchanged.

6. **Equilibrium Composition**: The addition of a catalyst does not change the equilibrium composition of the reactants and products. It only allows the system to reach equilibrium faster.

### Conclusion:
Based on the above analysis, we can conclude that:
- The equilibrium constant (Kc) will remain constant.
- The enthalpy change (ΔH) will remain constant.
- Kf and Kb will increase to the same extent.
- The equilibrium composition will not change.

Thus, the correct statements regarding the effect of the addition of a catalyst at constant temperature are:
- A: The equilibrium constant will remain constant.
- B: ΔH of the reaction will remain constant.
- C: Kf and Kb will increase to the same extent.
- D: The equilibrium composition will change (this statement is incorrect).