Reaction rate constant
In chemical kinetics a reaction rate constant or reaction rate coefficient, k, quantifies the rate of a chemical reaction.
For a reaction between reactants A and B to form product C
the reaction rate is often found to have the form:
Here k(T) is the reaction rate constant that depends on temperature. [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 instead moles of A or B per unit area).
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.
The Arrhenius equation gives the quantitative basis of the relationship between the activation energy and the reaction rate at which a reaction proceeds. The rate constant is then given by
and the reaction rate by
where 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 (not to be confused here with the reactant A).
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