Which of the following about the rate constant K of a reaction wrong ?

Options

A. it remains unchanged throughout the course of reaction
B. it provides a convenient measure of reaction rate
C. it is expressed in the same `unit(sec)^(1)` for all reactions
D. the more rapid the reaction, the larger is the value of K, the slower the reaction the smaller is its value

Answer

To determine which statement about the rate constant \( k \) of a reaction is incorrect, let's analyze each statement provided in the question:

1. **It remains unchanged throughout the course of the reaction.**
- This statement is **true**. The rate constant \( k \) is a characteristic of a particular reaction at a given temperature and does not change as the reaction proceeds.

2. **It provides a convenient measure of a reaction rate.**
- This statement is also **true**. The rate constant \( k \) is used in the rate law to relate the rate of a reaction to the concentrations of the reactants, thus providing a measure of the reaction rate.

3. **It is expressed in the same unit (second) for all the reactions.**
- This statement is **false**. The units of the rate constant \( k \) vary depending on the order of the reaction. For example, for a first-order reaction, the units are \( s^{-1} \), while for a second-order reaction, the units are \( L \cdot mol^{-1} \cdot s^{-1} \). Thus, this statement is incorrect.

4. **The more rapid the reaction, the larger the value of \( k \). The slower the reaction, the smaller is its value.**
- This statement is **true**. A larger value of \( k \) indicates a faster reaction, while a smaller value indicates a slower reaction.

### Conclusion:
The incorrect statement is: **"It is expressed in the same unit (second) for all the reactions."**