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Reaction rate constant
From Wikipedia, the free encyclopedia
In chemical kinetics a reaction rate constant quantifies the speed of a chemical reaction.
For a chemical reaction n A + m B → C + D, the reaction rate is typically of the form
![\frac{d[C]}{dt} = k(T)[A]^{n'}[B]^{m'}](../../../math/7/3/e/73e873ab1b9e6162a0c45659b62d0b52.png)
Here [X] denotes, for a reaction between liquids, gases, or solutes, the concentration of X; for a reaction taking place at a boundary it would denote something like moles of X per area.
In this equation k(T) is the reaction rate constant that depends on temperature.
The exponents n' and m' are called orders and depend on the reaction mechanism. In a single-step reaction can also be written as
![\frac{d[C]}{dt} = Ae^\frac{-E_a}{RT}[A]^n[B]^m](../../../math/0/6/e/06e3a7d1eaafc0fb495f2d2d0a3cc2e8.png)
Ea is the activation energy and R is the Gas constant. Since at temperature T the molecules have energies according to a Boltzmann distribution, one can expect the proportion of collisions with energy greater than Ea to vary with e-Ea/RT. A is the pre-exponential factor or frequency factor.
The Arrhenius equation gives the quantitative basis of the relationship between the activation energy and the reaction rate at which a reaction proceeds.