change of state

The state (solid, liquid, or gas) of a substance is not fixed but varies with changes in temperature and pressure.

In science, change in the physical state (solid, liquid, or gas) of a material. For instance, melting, boiling, and evaporation and their opposites, solidification and condensation, are changes of state. The former set of changes are brought about by heating or decreased pressure; the latter by cooling or increased pressure.

These changes involve the absorption or release of heat energy, called latent heat, even though the temperature of the material does not change during the transition between states. See also states of matter. Changes of state can be explained by the kinetic theory of matter. In the unusual change of state called sublimation, a solid changes directly to a gas without passing through the liquid state. For example, solid carbon dioxide (dry ice) sublimes to carbon dioxide gas.