Isfahan University of Technology Isfahan, Zip Code 84154, I.R. IRAN
A new model for the vapor phase of a pressurized liquid called "the cluster model: which is originally introduced in this work, along with an accurate equation of state for the liquid phase called the LIR, is used to derive an accurate equation for the vapor pressure of liquid as a function of external pressure. The chemical Potential of both phase have been found to be in good agreement with experiment. The calculated vapor pressure is compared with the Gibbs prediction. We have found that the Gibbs prediction is accurate at low external pressures and is reasonable at moderate pressures, but has a significant deviation at high external pressures. The calculated vapor pressure is used to obtain the vaporization enthalpy in terms of the external pressure. The physical interpretations for pressure dependence of both the vapor pressure and enthalpy of vaporization are also given. Compared to the temperature dependence, the pressure dependence of vapor pressure is insignificant.