Introductory Chemical Engineering Thermodynamics

Chapter 15. Phase Equilibria in Mixtures by an Equation of State

The whole is simpler than the sum of its parts.

J.W. Gibbs

Suppose it was required to estimate the vapor-liquid K-ratio of methane in a mixture at room temperature. For an initial guess, we might assume it follows ideal-solution behavior. It is a relatively simple molecule (e.g., no polar moments, no hydrogen bonding). But we cannot use Raoult’s law because the required temperature is well above the critical temperature. We could use Henry’s law, or the SCVP+ model (Section. 11.12), but the assumption of low concentrations may be inappropriate at very high pressures. The equation of state method discussed here is an attractive alternative.

We begin this chapter with a review of ...