phase rule

noun

, Physical Chemistry.

1. a law that the number of degrees of freedom in a system in equilibrium is equal to two plus the number of components less the number of phases. Thus, a system of ice, melted ice, and water vapor, being one component and three phases, has no degrees of freedom. Compare variance ( def 4 ).

phase rule

noun

1. the principle that in any system in equilibrium the number of degrees of freedom is equal to the number of components less the number of phases plus two See also degree of freedom component

phase rule

1. A rule used in thermodynamics stating that the number of degrees of freedom in a physical system at equilibrium is equal to the number of chemical components in the system minus the number of phases plus the constant 2.
2. Also called Gibbs phase rule
3. See also phase transition

Word History and Origins

Origin of phase rule¹

First recorded in 1895–1900

Example Sentences

The name of Willard Gibbs, who was the most distinguished American mathematical physicist of his day, is especially associated with the “Phase Rule,” of which some account will be found in the article Energetics.

From Project Gutenberg

The Phase Rule.—When the material system contains only a single phase, the number of independent variations, in addition to change of temperature and pressure, that can spontaneously occur in its constitution is thus one less than the number of its independent constituents.

From Project Gutenberg

By aid of this phase rule of Gibbs the number of different chemical substances actually interacting in a given complex system can be determined from observation of the degree of spontaneous variation which it exhibits; the rule thus lies at the foundation of the modern subject of chemical equilibrium and continuous chemical change in mixtures or alloys, and in this connexion it has been widely applied and developed in the experimental investigations of Roozeboom and van ’t Hoff and other physical chemists, mainly of the Dutch school.

From Project Gutenberg

Such graphical methods are now of fundamental importance in connexion with the phase rule, for the experimental exploration of the trend of the changes of constitution of complex mixtures with interacting components, which arise as the physical conditions are altered, as, for example in modern metallurgy, in the theory of alloys.

From Project Gutenberg

The question, moreover, has had a new light thrown upon it by the application of the principles of thermodynamics and of the phase rule.

From Project Gutenberg