ABSTRACT
Phase-equilibrium thermodynamics deals with the relationships that govern the distribution of a substance between gas and liquid phases. When a species is transferred from one phase to another, the rate of transfer generally decreases with time until the second phase is saturated with the species, holding as much as it can hold at the prevailing process conditions. When concentrations of all species in each phase cease to change, the phases are said to be at phase equilibrium. When two phases are brought into contact, a redistribution of the components of each phase occurs through evaporation, condensation, dissolution, and/or precipitation until a state of equilibrium is reached in which the temperatures and pressures of both phases are the same, and the compositions of each phase no longer change with time. The volatility of a species is the degree to which the species tends to be transferred from the liquid phase to the vapor phase. The vapor pressure of a species is a measure of its volatility. Estimation of vapor pressure can be carried out by empirical correlation.
