Incongruent transition, in

chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds made of atoms, molecules and ions ...

, is a mass transition between two phases which involves a change in

chemical composition A chemical composition specifies the identity, arrangement, and ratio of the elements making up a compound. Chemical formulas can be used to describe the relative amounts of elements present in a compound. For example, the chemical formula for ...

. 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 incre ...

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 phenomen ...

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 Ear ...

. 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

* {{refend Physical chemistry