In the presence of a catalyst, the heat evolved or absorbed during the reaction ………. .

Options

A. increases
B. decreases
C. reamains unchanged
D. may increases or decrease

Explanation

To solve the question, we need to understand the role of a catalyst in a chemical reaction, particularly in relation to the heat evolved or absorbed during the reaction.

### 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 providing an alternative reaction pathway with a lower activation energy.

**Hint**: Remember that a catalyst speeds up reactions but does not change the nature of the reactants or products.

2. **Effect on Reaction Rate**:
When a catalyst is added to a reaction, it lowers the activation energy barrier, allowing the reactants to convert to products more quickly. This means that the reaction reaches equilibrium faster.

**Hint**: Focus on how catalysts affect the speed of reaching equilibrium rather than changing the reaction itself.

3. **Heat of Reaction (ΔH)**:
The heat evolved or absorbed during a reaction is represented by ΔH (the change in enthalpy). This value is determined by the difference in energy between the reactants and products. Importantly, the addition of a catalyst does not alter the energy levels of the reactants or products.

**Hint**: ΔH is a property of the reaction itself and is not influenced by the presence of a catalyst.

4. **Conclusion**:
Since the catalyst does not change the enthalpy change (ΔH) of the reaction, the heat evolved or absorbed during the reaction remains unchanged regardless of the presence of the catalyst.

**Final Answer**: The heat evolved or absorbed during the reaction remains unchanged in the presence of a catalyst.

### Summary of the Answer:
The correct option is that the heat evolved or absorbed during the reaction remains unchanged when a catalyst is present.