7
I
N THE PREVIOUS CHAPTER, we introduced some important concepts
that we can apply to systems at equilibrium. The Clapeyron equation, the
Clausius-Clapeyron equation, and the Gibbs phase rule are tools that are used
to understand the establishment and changes of systems at equilibrium.
However, so far we have considered only systems that have a single chemical
component. This is very limiting, since most chemical systems of interest have
more than one chemical component. They are multiple-component systems.
We will consider multiple-component systems in two ways. One way will be
to extend some of the concepts of the previous chapter. We will do that only
in a limited fashion. The other way will be to build on the previous chapter’s
ideas and develop new ideas (and equations) that apply to multiple-component
systems. This will be our main approach.7.1 Synopsis
We start by extending the Gibbs phase rule to multiple-component systems, in
its most general form. We will confine our development of multiple-component
systems to relatively simple ones, having two or three components at most.
However, the ideas we will develop are generally applicable, so there will be
little need to consider more complicated systems here. One example of a sim-
ple two-component system is a mixture of two liquids. We will consider that,
as well as the characteristics of the vapor phase in equilibrium with the liquid.
This will lead into a more detailed study of solutions, where different phases
(solid, liquid, and gas) will act as either the solute or solvent.
The equilibrium behavior of solutions can be generalized by statements like
Henry’s law or Raoult’s law, and can be understood in terms of activity rather
than concentration. Changes in certain properties of all solutions can be under-
stood simply in terms of the number of solvent and solute particles. These
properties are called colligative properties.
Throughout the chapter, we will introduce new ways of graphically repre-
senting the behavior of multicomponent systems in an efficient visual way.
New ways of drawing phase diagrams, some simple and some complex, will be
presented.166
7.1 Synopsis
7.2 The Gibbs Phase Rule
7.3 Two Components:
Liquid/Liquid Systems
7.4 Nonideal Two-Component
Liquid Solutions
7.5 Liquid/Gas Systems and
Henry’s Law
7.6 Liquid/Solid Solutions
7.7 Solid/Solid Solutions
7.8 Colligative Properties
7.9 Summary