Pressure - Temperature (P-T, aka Phase State) 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, which is where the substance can simultaneously exist as a solid, a liquid, or a vapor.

P-T Diagram for a Substance That Expands On Freezing

Presure-Temperature (P-T, aka Phase) Diagram - RF Cafe

From	To	Phase Changes
Liquid	Solid	Fusion (aka Freezing)
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. It is the highest temperature at which a gas can be liquefied, regardless of pressure.
Triple Point:	Possible to maintain equilibrium mixture of all three phases.

Posted March 13, 2015

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