phase rule

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Related to phase rule: Phase diagram

phase rule

an expression of the relationships existing between systems in equilibrium: P + V = C + 2, where P is the number of phases, V the variance or degrees of freedom, and C the number of components; it also follows that the variance is V = C + 2 - P. For H₂O at its triple point, V = 1 + 2 - 3 = 0, that is, both temperature and pressure are fixed.

Synonym(s): Gibbs phase rule

References in periodicals archive ?

In general, correct solutions to the phase-mapping problem should follow the Gibbs phase rule, which specifies that the number of observed phases at a given chemical composition is no more than the number of chemical elements [N.sub.el]:

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According to the phase rule, when a second element is dissolved in aluminum, we have an additional degree of freedom.

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All TRC developments are built upon the algebraic constraints of the Gibbs phase rule, which specifies the number of free parameters necessary for a system to be thermodynamically well defined based on the number of chemical components and phases present.

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From a thermodynamic perspective, consider Gibb's phase rule (10) which tells us, for equilibrium conditions, the number of degrees of freedom, f, available to a system of c components when there are p coexisting phases present.

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The number of ways (degrees of freedom) in which temperature, pressure, or concentration can be varied in such cases can be expressed by a simple equation, which Gibbs called the phase rule. By the time he was through, Gibbs had left little more to do in what is now called chemical thermodynamics.