kT is the product of the Boltzmann constant, k, and the temperature, T. This product is used in physics as a scale factor for energy values in molecular-scale systems, as the rates and frequencies of many processes and phenomena depend not on their energy alone, but on the ratio of that energy and kT, that is, on E/kT. For a system in equilibrium in canonical ensemble, the probability of the system being in state with energy E is proportional to