Introduction

Phase diagrams come in many flavors but have features in common.  Generally, they describe the conditions under which certain phases can exist, either independently or in equilibrium with other phases.  A phase is a state of matter, solid, liquid or gas are examples of phases, and as we saw, it is possible to have more than one kind of solid phase or liquid phase (only in liquid helium).  In multi-component system, we keep this general description of phases and allow that in solutions, individual phases can have more than one component.  We need to refine our terminology just a bit for systems that contain impure phases.

Consitutent

A single chemical species.  For example, a mixture of alcohol and water consists of two constituents whereas aqueous sodium chloride has three (water, Na⁺ and Cl^–)

Component

a chemically independent constituent is a component.  If there is no chemical reaction then the components are all constituents.

Example,

consider the reaction	CaCO3(s)	CaO(s)  +	CO2(g)
There are three phases	1	2	3
there are three constituents	1	2	3
there are two components	1	2	not independent as the reaction chemistry can tell us of this phase.

Phase Diagrams

Liquid Liquid

Solid Liquid

Ternary