Distinguish between 'rate expression' and 'rate constant' of a reaction.

Explanation

To distinguish between 'rate expression' and 'rate constant' of a reaction, we can break down the definitions and characteristics of each term.

### Step-by-Step Solution:

1. **Definition of Rate Expression**:
- The rate expression is a mathematical representation of the rate of a chemical reaction. It relates the rate of the reaction to the concentrations of the reactants.
- It is expressed as:
\[
...