A chemical reaction is catalysed by a catalyst hence the catalyst 

Options

A. increases the activation energy
B. does not effect the equilibrium constant of a reaction
C. reduces enthalpy of the reaction
D. decreases rate constant of the reaction

Answer

To solve the question regarding the role of a catalyst in a chemical reaction, we will analyze each provided option step by step.

### Step-by-Step Solution:

1. **Understanding the Role of a Catalyst**:
- A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the process. It achieves this by providing an alternative pathway for the reaction with a lower activation energy.

2. **Analyzing the Options**:
- **Option A: It increases the activation energy.**
- This statement is incorrect. A catalyst actually decreases the activation energy, which facilitates the reaction to occur more quickly.

- **Option B: It does not affect the equilibrium constant of the reaction.**
- This statement is correct. A catalyst speeds up both the forward and reverse reactions equally, thus it does not change the position of equilibrium or the equilibrium constant.

- **Option C: It reduces the enthalpy of the reaction.**
- This statement is incorrect. A catalyst does not change the enthalpy of the reaction; it only affects the rate at which equilibrium is reached.

- **Option D: It decreases the rate constant of the reaction.**
- This statement is incorrect. A catalyst increases the rate constant of the reaction, leading to an increased rate of both the forward and backward reactions.

3. **Conclusion**:
- After evaluating all options, the correct answer is **Option B: It does not affect the equilibrium constant of the reaction**.

### Final Answer:
The correct option is **B**: It does not affect the equilibrium constant of the reaction.

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