A General Internal Potential Including Molecular Volume. Internal Energy and Equation of State of Fluids in Gas and Liquid Phases and under Critical Conditions: Study over a Wide Range of Temperature and Pressure

Abstract

The energy of molecular interaction for all fluids is represented by means of a single relation which takes into account both the excluded volume V τ and the free volume (V − V τ). From this expression, we obtain a single equation of state which is in very close agreement with the representation of experimental results for all fluids both in the liquid and gaseous phase and over wide ranges of temperature and pressure. The generalisation of the study on different fluids allows following the variation of the excluded volume V τ as function of molar volume and temperature. This variation, which we write as (∂V τ/∂V) T , becomes pronounced in the neighbourhood of critical conditions. It must be taken into consideration in the explanation of observed anomalies of the pressure and C v near critical conditions.