In a previous work [E.M. Prodanov, R.I. Ivanov, and V.G. Gueorguiev, 2007], we proposed a classical model for the expansion of the Universe during the radiation-dominated epoch based on the gravitational repulsion of the Reissner-Nordström geometrynaked singularity description of particles that "grow" with the drop of the temperature. In this work we model the Universe during the Reissner-Nordström expansion as a van der Waals gas and determine the equation of state.