https://doi.org/10.1351/goldbook.C00789
The
rate constant
for a system in which the reactants
are in thermal equilibrium at a given temperature. In statistical mechanics the expression 'canonical ensemble' is used to refer to a closed system in thermal equilibrium, the species being present in a statistical distribution. By contrast, a microcanonical ensemble is composed of systems all having the same energy: a canonical ensemble therefore consists of a statistical distribution of microcanonical ensembles. The canonical or thermal rate constant
can be obtained from the microcanonical rate constant
by summing over the energy, taking into account the statistical distribution.