In addition to its importance as a property of the fluid, the cavity formation energy (CFE),may also be viewed as the first step of solvation process [1]. The analytical expression for the CFE in a hard sphere (HS) fluid is available from the scaled particle theory (SPT) [2] as well as Boublik-Mansoori-Carnahan-Starling-Leland (BMCSL) equation of state for HS mixtures [3]. In this work we present a unique and exact analytical expression for the heat of vaporization ( vap H ∆ ) based on the CFE expression. The validity of different CFE models is then examined by using the experimental values of vap H ∆ instead of the predicted values of CFE by computer simulation approaches [4]. Therefore the hidden deviations in the CFE due to the enthalpy-entropy compensation are revealed by vap H ∆ expression. This expression is also used for prediction of the effective molecular hard-core diameter at different temperatures and pressures.
