phase rule 

https://doi.org/10.1351/goldbook.P04533
The number of degrees of freedom, F, that a system containing C components can have when P phases are in equilibrium, is given as: F=C−P+2
Source:
PAC, 1994, 66, 577. (Definitions of terms relating to phase transitions of the solid state (IUPAC Recommendations 1994)) on page 588 [Terms] [Paper]
Citation: 'phase rule' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.P04533 RIS BibTex EndNote
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Last revised: February 24, 2014