Reaction rate constant

In chemical kinetics, a reaction rate constant or reaction rate coefficient (⁠${\displaystyle k}$⁠) is a proportionality constant which quantifies the rate and direction of a chemical reaction by relating it with the concentration of reactants.^[1]

For a reaction between reactants A and B to form a product C,

where

A and B are reactants

C is a product

a, b, and c are stoichiometric coefficients,

the reaction rate is often found to have the form:

$${\displaystyle r=k[\mathrm {A} ]^{m}[\mathrm {B} ]^{n}}$$

Here ⁠${\displaystyle k}$⁠ is the reaction rate constant that depends on temperature, and [A] and [B] are the molar concentrations of substances A and B in moles per unit volume of solution, assuming the reaction is taking place throughout the volume of the solution. (For a reaction taking place at a boundary, one would use moles of A or B per unit area instead.)

The exponents m and n are called partial orders of reaction and are not generally equal to the stoichiometric coefficients a and b. Instead they depend on the reaction mechanism and can be determined experimentally.

Sum of m and n, that is, (m + n) is called the overall order of reaction.