Incongruent transition, in
chemistry, is a mass transition between two
phases which involves a change in
chemical composition. This is contrasted with congruent transition, for which the composition remains the same.
The transition may be that of
melting
Melting, or fusion, is a physical process that results in the phase transition of a substance from a solid to a liquid. This occurs when the internal energy of the solid increases, typically by the application of heat or pressure, which inc ...
,
vaporization
Vaporization (or vaporisation) of an element or compound is a phase transition from the liquid phase to vapor. There are two types of vaporization: evaporation and boiling. Evaporation is a surface phenomenon, whereas boiling is a bulk phenomenon ...
or
allotropism. The concept is also often extended to related phenomena, for example,
incongruent dissolution of a solid by a liquid solvent, which is often encountered in
geology
Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Ea ...
.
The term "phase decomposition" is sometimes used to describe incongruent transition. However, it has to be kept in mind that incongruent transition is described by an
equilibrium.
For an example, see
incongruent melting
Incongruent melting occurs when a solid substance does not melt uniformly, so that the chemical composition of the resulting liquid is not the same as that of the original solid. During incongruent melting a new solid of different composition form ...
.
References
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Physical chemistry