Gibbs' Phase Rule Calculator

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The minimum number of chemically independent species needed to describe all phases. For a pure substance C = 1; for a binary mixture C = 2.
A phase is a homogeneous, physically distinct region of matter. Count each distinct solid polymorph, liquid layer, and the gas phase separately.
Number of stoichiometrically independent chemical reactions among the species. Set to 0 for nonreactive (or single-species) systems.
If the system is held at a fixed temperature (e.g. in a thermostat), subtract 1 from the unconstrained result.
If the system is held at a fixed pressure (e.g. open to the atmosphere), subtract 1 from the unconstrained result.
Degrees of freedom (F)Multivariant
3

Number of intensive variables that can be changed independently without altering the number of phases

System varianceMultivariant (F = 3)
Pressure-temperature factor2
3
Invariant (F=0)<1Univariant (F=1)1-2Divariant (F=2)2-3Multivariant (F≥3)3+

F = 3: this system is multivariant (f = 3).

  • With 3 degrees of freedom, you can independently specify 3 intensive variables (e.g. temperature, pressure, or 1 independent composition ratios) and still maintain the same number of phases.
  • For this component count (C = 2) and reaction count (r = 0) at factor = 2, the maximum number of co-existing phases at equilibrium is 4.

Next stepYou can independently specify 3 intensive variables (e.g. temperature, pressure, or mole fractions) to define the equilibrium state.

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