An enzyme promotes a chemical reaction by

Options

A. a) lowering the energy of activation
B. b) changing the free energy difference between substrate and product
C. c) increasing molecular motion
D. d) All of these

Answer

To solve the question "An enzyme promotes a chemical reaction by," we will analyze the options provided:

1. **Understanding Enzymes**: Enzymes are biological catalysts that speed up chemical reactions in living organisms. They do this by lowering the activation energy required for the reaction to occur.

2. **Analyzing the Options**:
- **Option A: Lowering the energy of activation**: This is true. Enzymes work by providing an alternative pathway for the reaction that has a lower activation energy.
- **Option B: Changing the free energy difference between the substrate and product**: This is false. Enzymes do not change the overall free energy difference between the reactants and products; they only affect the rate at which equilibrium is reached.
- **Option C: Increasing molecular motion**: While enzymes may influence the molecular interactions, they do not directly increase molecular motion. Instead, they stabilize the transition state.
- **Option D: All of the above**: Since options B and C are incorrect, this option cannot be true.

3. **Conclusion**: The correct answer is **Option A: Lowering the energy of activation**. Enzymes facilitate reactions by decreasing the activation energy, thereby increasing the rate of the reaction without altering the overall energy change of the reaction.