Introductory Chemical Engineering Thermodynamics

Chapter 9. Phase Equilibrium in a Pure Fluid

One of the principal objects of theoretical research is to find the point of view from which it can be expressed with greatest simplicity.

J.W. Gibbs (1881)

The problem of phase equilibrium is distinctly different from “(In – Out) = Accumulation.” The fundamental balances were useful in describing many common operations like throttling, pumping, and compressing, and fundamentally, they provide the basis for understanding all processes. But the balances make a relatively simple contribution in solving problems of phase equilibrium—so much so that they are largely ignored, while simple questions like “How many phases are present?” take the primary role.

The general problem of phase equilibrium has a ...