Equipartition of Energy

a principle of classical statistical mechanics stating that a statistical system in a state of thermodynamic equilibrium has an average kinetic energy of kT/2 associated with each translational and rotational degree of freedom and an average energy of kT associated with each vibrational degree of freedom. Here, T is the absolute temperature of the system and k is the Boltzmann constant. The equipartition principle is an approximate law. It breaks down when quantum effects become important or, in the case of vibrational degrees of freedom, when the anharmonic terms of the interaction become significant. The equipartition principle permits the maximum values of the specific heats of polyatomic gases and solids at high temperatures to be easily estimated.