# Difference Between Rate Constant and Rate Expression

This lesson will teach you the difference between rate constant and rate expression in chemistry. A reaction’s rate is determined by its kinetic order, which is expressed as a ratio of reactant concentrations. The two most common ways to express rates are with an equation or a graph.

Rate expression and rate constant are two different ways to express the same thing. Rate expression is a mathematical equation that relates the rate of change in concentration or pressure with respect to time. A rate expression can be used as an input for a differential equation, which will give you the result.

The first term on the right-hand side of this equation would represent “rate.” Rate constants only tell you how fast something happens over a period of time and does not include any information about what caused it, so they cannot be used as inputs for equations like these.

The difference between rate constants and rate expressions is that one tells you how fast something happened over a period of time while the other includes information about what caused it.

**Rate** Expression

- It is a mathematical expression of the rate of a chemical reaction.
- It is represented by Rate = k [Reactant].

## Rate Constant

- It is proportionality constant in the rate expression.
- It is represented by ‘K’.