A van der Waals approach to the entropy convergence phenomenon

Abstract

The van der Waals approach for the excluded volume effect is used to calculate the thermodynamics of cavity creation in a liquid. By using the experimental density of c-hexane, benzene and water and a temperature independent hard sphere diameter for solvent molecules, the van der Waals approach leads to the following results: (a) the values of the work of cavity creation show a linear decrease in the two organic solvents, but a parabolic temperature dependence with a maximum around 170 °C in water; (b) the cavity entropy changes are positive and practically independent of temperature in the two organic solvents; (c) the cavity entropy changes in water are large negative at room temperature and then increase showing the convergence phenomenon at 160 °C. Therefore, the experimental density of solvents at each temperature and the hard sphere diameter of solvent molecules considered to be temperature independent are sufficient to distinguish water from c-hexane and benzene and to reproduce entropy convergence.