Which of the following reaction parameters will change due to addition of a catalyst ?

Options

A. Free energy
B. Only equilibrium constant
C. Only rate constant
D. Both equilibrium constant and rate constant

Answer

To solve the question regarding which reaction parameter changes due to the addition of a catalyst, we can follow these steps:

### Step 1: Understand 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 reaction pathway with a lower activation energy.

**Hint:** Remember that a catalyst does not change the overall energy of the reactants and products but lowers the energy barrier for the reaction.

### Step 2: Identify the reaction parameters
The common reaction parameters include:
- Rate of reaction
- Activation energy
- Equilibrium constant
- Rate constant

**Hint:** Think about how each of these parameters is affected by the presence of a catalyst.

### Step 3: Analyze the effect of a catalyst on these parameters
1. **Rate of reaction**: A catalyst increases the rate of reaction by lowering the activation energy.
2. **Activation energy**: This is directly affected by the catalyst, as it lowers the activation energy required for the reaction to proceed.
3. **Equilibrium constant**: The equilibrium constant remains unchanged because it is dependent on the free energy difference between reactants and products, which is not altered by a catalyst.
4. **Rate constant**: The rate constant increases because it is related to the activation energy. A lower activation energy results in a higher rate constant.

**Hint:** Focus on how the catalyst specifically alters the energy barriers and the rate at which the reaction occurs.

### Step 4: Conclusion
From the analysis, we can conclude that the addition of a catalyst affects the rate constant and the rate of reaction, but it does not change the equilibrium constant.

Thus, the correct answer to the question is that the **rate constant** will change due to the addition of a catalyst.

**Final Answer:** Option C is correct.