A catalyst increases the rate of a reaction by:

Options

A. (a) increasing the activation energy of a reaction
B. (b) decreasing the activation energy
C. (c) increasing the enthalpy change of the reaction
D. (d) decreasing the enthalpy change of the reaction

Answer

To solve the question "A catalyst increases the rate of a reaction by:", we will analyze the options provided and understand the role of a catalyst in chemical reactions.

### Step-by-Step Solution:

1. **Understanding Activation Energy**:
- Activation energy (EA) is the minimum energy required for reactants to undergo a chemical reaction. It is the energy barrier that must be overcome for the reaction to proceed.

2. **Graphical Representation**:
- We can visualize the reaction using a potential energy diagram. In this diagram:
- The y-axis represents energy.
- The x-axis represents the progress of the reaction.
- The curve shows the energy of the reactants and products, with a peak representing the activation energy barrier.

3. **Role of a Catalyst**:
- A catalyst is a substance that increases the rate of a reaction without being consumed in the process. It achieves this by providing an alternative pathway for the reaction with a lower activation energy.
- In the energy diagram, the presence of a catalyst lowers the height of the activation energy barrier.

4. **Evaluating the Options**:
- **Option A: Increasing activation energy** - This is incorrect because a catalyst does not increase the activation energy; it decreases it.
- **Option B: Decreasing activation energy** - This is correct. A catalyst lowers the activation energy, allowing more reactant molecules to have sufficient energy to react.
- **Option C: Increasing the enthalpy change of the reaction** - This is incorrect. A catalyst does not change the enthalpy change (ΔH) of the reaction.
- **Option D: Decreasing the enthalpy change for the reaction** - This is also incorrect for the same reason as option C.

5. **Conclusion**:
- The correct answer is **Option B: Decreasing activation energy**. A catalyst increases the rate of a reaction by lowering the activation energy required for the reaction to occur.