Density is defined as the mass per unit volume for a substance. For vapors the density is a function of composition, temperature and pressure and can be accurately predicted by an equation of state. For ideal gaseous mixtures, interaction of the components is negligible and the density may be determined with the ideal gas law as a function of temperature and pressure only.
The most common method to evaluate vapor density in PRO/II is with one of the equations of state. Available methods for calculating vapor density are listed below.