Harper's Illustrated Biochemistry, Volume 1 - Murray R. 1993

Structure and Function of Proteins and Enzymes
Enzymes: Kinetics
Reactant Concentration

As the concentration of reactants increases, both the number of molecules possessing sufficient energy for the reaction and the frequency of their collisions increase. Let us consider a reaction between two different molecules A and B:

Class="center">А + В → AB.

Doubling the concentration of either A or B will double the reaction rate, while simultaneously doubling the concentrations of both A and B will increase the probability of their collisions fourfold. Consequently, the reaction rate will increase four times. The reaction rate is proportional to the concentrations of the reacting molecules. Square brackets are used to denote molar concentrations1, and the symbol $\propto$ denotes proportionality. The rate expression takes the form

For the reaction

А + 2В → AB,

the reaction rate expression has the form

In the general case, when n molecules of A react with m molecules of B,

nА + mВ → АnВm,

the expression for the reaction rate takes the form Rate ∝ [А]n[В]m.



Last update: 06/08/2026

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