ABSTRACT
This chapter examines the equilibrium between phases, and the factors affecting the equilibrium state, for one-component and non-reactive two-component systems. The chemical composition of non-reactive systems is expressed in terms of components, which are the chemically independent constituents comprising a system. It follows that the composition of phases comprising a system can also be expressed in terms of the components of the system as a whole. The phase rule is a tool which enables us to examine and greatly simplify the complex nature of multi-component, multi-phase systems. A one-component system consists of one pure substance. Pure substances can exist in three states – solid, liquid and gas. The effects of temperature, pressure and composition on the phases which exist at equilibrium can be represented graphically, but while three-dimensional phase diagrams can be constructed, particularly with the aid of computer graphics, they are often difficult to visualise and interpret.
