Editing Phase transition (section)

===States of matter===
[[File:Phase diagram of water simplified.svg|thumb|250px|A simplified phase diagram for [[water]], showing whether solid ice, liquid water, or gaseous water vapor is the most stable at different combinations of temperature and pressure.]]
{{See also|vapor pressure|phase diagram}}

Phase transitions commonly refer to when a substance transforms between one of the four [[state of matter|states of matter]] to another. At the phase transition point for a substance, for instance the [[boiling point]], the two phases involved - liquid and [[vapor]], have identical free energies and therefore are equally likely to exist. Below the boiling point, the liquid is the more stable state of the two, whereas above the boiling point the gaseous form is the more stable. 

Common transitions between the solid, liquid, and gaseous phases of a single component, due to the effects of temperature and/or [[pressure]] are identified in the following table:
{{Table of Phase Transitions}}

For a single component, the most stable phase at different temperatures and pressures can be shown on a [[phase diagram]]. Such a diagram usually depicts states in equilibrium. A phase transition usually occurs when the pressure or temperature changes and the system crosses from one region to another, like water turning from liquid to solid as soon as the temperature drops below the [[freezing point]]. In exception to the usual case, it is sometimes possible to change the state of a system [[Adiabatic|diabatic]]ally (as opposed to [[adiabatic invariant|adiabatic]]ally) in such a way that it can be brought past a phase transition point without undergoing a phase transition. The resulting state is [[metastable]], i.e., less stable than the phase to which the transition would have occurred, but not unstable either. This occurs in [[superheating]] and [[supercooling]], for example. Metastable states do not appear on usual phase diagrams.