Reaction rate constant

In chemical kinetics a reaction rate constant quantifies the speed of a chemical reaction.

For a chemical reaction k A + m B → C + D, the reaction rate is typically of the form

$\frac{d[C]}{dt} = k(T)[A]^{k'}[B]^{m'}$

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 per area of X.

In this equation k(T) is the reaction rate constant that depends on temperature.

The exponents k' and m' are called orders and depend on the reaction mechanism. In a single-step reaction can also be written as

$\frac{d[C]}{dt} = ke^\frac{-E_a}{RT}[A]^k[B]^m$

E_a 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 E_a to vary with e^-Ea/RT. K 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.

Categories: Physical chemistry