During the course of a chemical reaction , the rate constant ___.

Options

A. Remains constant throughout
B. Increases as the reaction proceeds
C. Decreases as the reaction proceeds
D. First increases followed by a decreases

Answer

**Step-by-Step Solution:**

1. **Understanding the Rate Constant**: The rate constant (k) is a proportionality factor in the rate law expression of a chemical reaction. It relates the rate of the reaction to the concentration of the reactants.

2. **Rate Law Expression**: For a general reaction, the rate of reaction (R) can be expressed as:
\[ R = k[A]^n \]
where [A] is the concentration of reactant A and n is the order of the reaction.

3. **Definition of Rate Constant**: The rate constant is defined as the rate of reaction when the concentration of the reactant is unity (1 mol/L). This means that the rate constant is a characteristic of the reaction at a given temperature.

4. **Behavior During the Reaction**: As the reaction proceeds, the concentration of the reactant A decreases while the concentration of the product B increases. However, the rate constant (k) is independent of the concentration of reactants.

5. **Conclusion**: Since the rate constant does not depend on the concentration of reactants and remains unchanged during the course of the reaction, we conclude that the rate constant remains constant throughout the reaction.

**Final Answer**: The rate constant remains constant throughout the course of the chemical reaction.

---