A catalyst cannot change

Options

A. Rate constant of the reaction
B. Equilibrium constant of the reaction
C. Activation energy of reaction
D. All of these

Answer

**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 lowering the activation energy (Ea) required for the reaction to proceed.

2. **Effect on Activation Energy:**
When a catalyst is introduced to a reaction, it provides an alternative pathway with a lower activation energy. This means that more molecules have sufficient energy to overcome the energy barrier, leading to an increased rate of reaction.

3. **Impact on Rate Constant:**
The rate constant (k) of a reaction is related to the activation energy by the Arrhenius equation:
\[ k = A e^{-\frac{E_a}{RT}} \]
Here, A is the pre-exponential factor, \(E_a\) is the activation energy, R is the gas constant, and T is the temperature. Since a catalyst lowers \(E_a\), it directly affects the rate constant, increasing its value.

4. **Effect on Equilibrium Constant:**
The equilibrium constant (K) of a reaction is determined by the ratio of the concentrations of products to reactants at equilibrium. A catalyst does not change the position of equilibrium; it only helps the system reach equilibrium faster. Therefore, the equilibrium constant remains unchanged.

5. **Conclusion:**
Based on the above points, we can conclude that a catalyst does not change the equilibrium constant of a reaction. It affects the rate constant and lowers the activation energy but does not alter the equilibrium constant.

**Final Answer:**
A catalyst cannot change the equilibrium constant.

---