The addition of a catalyst during a chemical reaction alters which of the following quantities ?

Options

A. Internal energy
B. Enthalpy
C. Activation energy
D. Entropy

Explanation

To determine which quantity is altered by the addition of a catalyst during a chemical reaction, we can analyze the options provided: internal energy, enthalpy, activation energy, and entropy.

### 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 itself undergoing any permanent chemical change. It achieves this by providing an alternative reaction pathway with a lower activation energy.

2. **Analyzing the Given Quantities**:
- **Internal Energy**: This is the total energy contained within a system. The addition of a catalyst does not change the internal energy of the reactants or products.
- **Enthalpy**: This is the heat content of a system at constant pressure. A catalyst does not alter the enthalpy change of the reaction; it remains the same regardless of the presence of a catalyst.
- **Activation Energy**: This is the minimum energy required for a reaction to occur. A catalyst lowers the activation energy, making it easier for the reaction to proceed.
- **Entropy**: This is a measure of the disorder or randomness in a system. The addition of a catalyst does not affect the entropy of the reactants or products.

3. **Conclusion**:
- The only quantity that is altered by the addition of a catalyst is the **activation energy**. By lowering the activation energy, the catalyst increases the rate of the reaction.

### Final Answer:
The addition of a catalyst during a chemical reaction alters the **activation energy**.

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