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phase rule

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
1895-1900
1895-1900
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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Examples from the web for phase rule
  • The execution may terminate and indicate that a phase rule violation has occurred, or may simply remove one of the variables.
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 two See also degree of freedom, component (sense 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
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phase rule in Science
phase rule  
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 © 2002. Published by Houghton Mifflin. All rights reserved.
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Encyclopedia Article for phase rule

law relating variables of a system in thermodynamic equilibrium, deduced by the American physicist J. Willard Gibbs in his papers on thermodynamics (1875-78). Systems in thermodynamic equilibrium are generally considered to be isolated from their environment in some kind of closed container, but many geological systems can be considered to obey the phase rule. The variables are: the number of phases P (forms of matter; i.e., solid, liquid, and gas not necessarily of a single chemical component), the number of chemical components C (pure compounds or elements), and the number of degrees of freedom F of intensive variables, such as temperature, pressure, and percentage composition. The phase rule states that F = C - P + 2. Thus, for a one-component system with one phase, the number of degrees of freedom is two, and any temperature and pressure, within limits, can be attained. With one component and two phases-liquid and vapour, for example-only one degree of freedom exists, and there is one pressure for each temperature. For one component and three phases (e.g., ice floating in water with water vapour above it, in a closed container), there is no degree of freedom, and temperature and pressure are both fixed at what is called the triple point (see phase diagram).

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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