How this calculator works
The phase rule counts independent intensive variables for an equilibrium system with no extra fields or special restrictions. Components are the minimum independent chemical constituents after accounting for reactions, not automatically the number of named species. Fixing temperature or pressure removes a degree of freedom only when the imposed condition is independent and compatible with phase coexistence. Negative freedom signals incompatible assumptions, rather than a physical negative count.
Formula
F = C - P + 2 - q, where q is the number of independent fixed intensive constraints (0, 1 or 2).
Worked example
One component in three coexisting phases has F = 1 - 3 + 2 = 0. Two components in one phase with one independent variable fixed have F = 2 - 1 + 2 - 1 = 2.
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Frequently asked questions
What is a component?
It is an independent constituent needed to specify composition after chemical constraints are applied.
Can I always fix both temperature and pressure?
Only if the resulting conditions are compatible and independent; an invariant equilibrium may already determine both.
Are phases the same as chemical species?
No. Several species can share one homogeneous phase.