# What is rate constant?

The rate constant is defined as the proportionality constant which explains the relationship between the molar concentration of the reactants and the rate of a chemical reaction.

The rate constant is denoted by k and is also known as reaction rate constant or reaction rate coefficient. It is dependent on the temperature.

There are two possible ways to calculate rate constant and they are:

1. Using the Arrhenius equation.
2. Using the molar concentrations of the reactants and the order of the reaction.

## Unit of the rate constant

Unit of the rate constant is dependent on the order of reaction and is given:

 Zero-order reaction mol.L-1.s-1 First-order reaction s-1 Second-order reaction M-1.s-1 Third-order reaction M-2.s-1

Following are the ways to express rate constant:

k =

$$\begin{array}{l}\frac{Rate}{[A]^{a}[B]^{b}}\end{array}$$

Where,

• k is the rate constant
• [A] and [B] are the molar concentration of reactants A and B
• a and b are the order of the reaction.

Rate constant from the Arrhenius equation

$$\begin{array}{l}k=Ae^{\frac{-Ea}{RT}}\end{array}$$

Where,

• A is the frequency of particle collision
• Ea is the activation energy
• R is the universal gas constant
• T is the absolute temperature