In a chemical reaction , a catalyst used for

Options

A. Decreases the energy of activation
B. Increases the energy of activation
C. Does not change energy of activation
D. Decreases or increases the energy of activation

Answer

To solve the question regarding the role of a catalyst in a chemical reaction, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Role of a Catalyst**:
- A catalyst is a substance that increases the rate of a chemical reaction without undergoing any permanent change itself.

2. **Identify Activation Energy**:
- Activation energy (Ea) is the minimum energy required for a reaction to occur. It is the energy barrier that must be overcome for reactants to be transformed into products.

3. **Graphical Representation**:
- To visualize the effect of a catalyst, we can plot a graph with the reaction coordinate (progress of the reaction) on the x-axis and energy on the y-axis.
- In the graph, we will have two curves: one for the uncatalyzed reaction and one for the catalyzed reaction.

4. **Uncatalyzed Reaction**:
- The curve representing the uncatalyzed reaction will show a higher activation energy (Ea). This is the energy barrier that must be overcome for the reaction to proceed.

5. **Catalyzed Reaction**:
- The curve representing the catalyzed reaction will show a lower activation energy (Ea'). The presence of the catalyst provides an alternative pathway for the reaction, which requires less energy.

6. **Comparison of Activation Energies**:
- By comparing the two activation energies, we can conclude that the activation energy decreases when a catalyst is used (Ea' < Ea).

7. **Conclusion**:
- Therefore, the correct option is that a catalyst decreases the energy of activation.

### Final Answer:
A catalyst decreases the energy of activation in a chemical reaction.