The Next Level of Complexity in Phase Equilibrium

The simplest possible phase equilibrium is that between a pure liquid and the corresponding gas or vapor. 

We may profitably think of this as a situation in which the rate of escape of molecules from the liquid surface is 

FIGURE 3.4 If we place a suitable amount of pure H2O in a rigid adiabatic container and wait for equilibrium, we will eventually find steam and liquid water, both at the same temperarnre and pressure (except for the very small pressure differences caused by gravity and surface tension). 

In Chapter 5 we will see that the Antoine equation (Eq. 5.12) represents experimental vapor-pressure data with reasonable accuracy in a simple algebraic form. It is shown, along with suitable values for a variety of chemicals, in Appendix A.2. We will use it in this chapter, while deferring the discussion of its origin until Chapter 5. 

THE SIMPLEST PHASE EQUILIBRIUM EXAMPLES AND SOME SIMPEE ESTIMATING RULES 

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