Pressure - Temperature (P-T) Diagram

A common graphic used to illustrate the relationship of substances in their phase states as a function of pressure and temperature is the P-T diagram. It is also referred to as a phase state diagram or a phase change diagram. The asterisk in the P-T diagram below identifies a pressure-temperature combination that is known as the triple point. That is where the substance can exist as a solid, a liquid, or a vapor.

P-T Diagram for a Substance That Expands On Freezing

From	To	Phase Changes
Liquid	Solid	Fusion
Liquid	Vapor	Vaporization
Solid	Vapor	Sublimation
Solid	Liquid	Melting
Vapor	Liquid	Condensation
Vapor	Solid	Deposition

. Critical      Point:	Pure vapor phase has same properties as pure liquid phase at same temperature and pressure.
* Triple      Point:	Possible to maintain equilibrium mixture of all three phases.