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. |