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phase rule

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noun Physical Chemistry.
  1. a law that the number of degrees of freedom in a system in equilibrium is equal to two plus the number of components less the number of phases. Thus, a system of ice, melted ice, and water vapor, being one component and three phases, has no degrees of freedom.Compare variance(def 4).

Origin of phase rule

First recorded in 1895–1900
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for phase rule

phase rule

noun
  1. the principle that in any system in equilibrium the number of degrees of freedom is equal to the number of components less the number of phases plus twoSee also degree of freedom, component (def. 4)
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

phase rule in Science

phase rule

  1. A rule used in thermodynamics stating that the number of degrees of freedom in a physical system at equilibrium is equal to the number of chemical components in the system minus the number of phases plus the constant 2. Also called Gibbs phase rule See also phase transition state of matter.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.