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 =

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


  • 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

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


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

Articles to Explore:

  1. What is the difference between the rate of reaction and the reaction rate constant?
  2. Definition Of Rate Law

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