Gibbs phase rule


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Gibbs phase rule

n. Physics
A rule stating that the number of degrees of freedom in a closed physical system at equilibrium is equal to the number of chemical components minus the number of phases plus the constant 2. For example, the system of water vapor, liquid water, and solid ice has zero degrees of freedom because the three phases of vapor, liquid, and solid coexist in the one component, water. Also called phase rule.

[After Josiah Willard Gibbs.]
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
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One important precept is the Gibbs phase rule, which limits the number of phases present to at most k phases per sample point, in a system involving k elements.
According to the Gibbs phase rule, a maximum of three phases can coexist in equilibrium under the conditions of constant pressure and temperature (T, p = const) in a three-component system.
The dotted lines in (20, [ILLUSTRATION FOR FIGURES 7 AND 8 OMITTED]) are required to satisfy the Gibbs phase rule.