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 ?
According to the phase rule, when a second element is dissolved in aluminum, we have an additional degree of freedom.
In order to ensure a well defined thermodynamic state and to prevent storage of dependent variables as independent, the system is constrained according to the Gibbs Phase Rule.
explains the mathematics involved, then covers the first through third laws of thermodynamics, enthalpy, heat capacity, applications of the first law to gases, equilibrium and spontaneity for systems of constant temperature, the Gibbs function and the Planck function, the thermodynamics of systems of variable composition, applications of the Gibbs function to chemical changes, the phase rule, the ideal solution, determination of nonelectrolyte activities and excess Gibbs functions from experimental data, calculation of partial molar quantities and excess molar quantities from experimental data, strong electrolytes, changes for Gibbs function for processes in solutions, systems subject to a gravitational or a centrifugal field and estimation of thermodynamic quantities.
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.
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.