A catalyst increases the rate of reaction * but does not participate.

Answer

To explain the statement "A catalyst increases the rate of reaction but does not participate," we can break it down into several steps:

### Step-by-Step Solution:

1. **Definition of a Catalyst**:
- A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the process. This means that at the end of the reaction, the catalyst is still present and unchanged.

2. **Mechanism of Action**:
- While a catalyst may interact with reactants during the reaction, it does not undergo any permanent change. It can temporarily combine with reactants to form an intermediate, but this is a reversible process.

3. **Lowering Activation Energy**:
- One of the primary roles of a catalyst is to provide an alternative pathway for the reaction that has a lower activation energy compared to the uncatalyzed reaction. Activation energy is the minimum energy required for a reaction to occur.

4. **Effect on Reaction Rate**:
- By lowering the activation energy, a catalyst allows more reactant molecules to have sufficient energy to undergo the reaction, thus increasing the rate at which products are formed.

5. **Regeneration of the Catalyst**:
- After the reaction has occurred, the catalyst is regenerated and can be used again for subsequent reactions. This characteristic distinguishes catalysts from reactants, which are consumed during the reaction.

### Summary:
In summary, a catalyst increases the rate of a reaction by providing an alternative pathway with lower activation energy, allowing the reaction to proceed more quickly. However, it does not participate in the reaction in a way that changes its own structure permanently, as it is regenerated at the end.

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