Exact Dynamical Basis for a Fluctuating Cell Model

Cell‐like models for many‐body thermodynamic properties can be derived by considering the motion of a single very light particle in a classical system. Because the configuration probabilities are mass independent, the pressure and the energy calculated for such a light particle are identical with thermodynamic values. In the special case of hard spheres it is shown that the pressure from collisions is proportional to the surface‐to‐volume ratio of the hard sphere free volume.