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Purpose of Residual property and Excess property in Thermodynamics

  1. Dec 3, 2007 #1
    Can anybody tell me what are Residual property and Excess property in thermodynamics for?
    Last edited: Dec 3, 2007
  2. jcsd
  3. Dec 3, 2007 #2


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    Residual functions are used to calculate properties of substances at non ideal gas states. I have never heard of the Excess property myself. Perhaps someone else can answer that for you.

    Hopefully this link works:
    http://books.google.com/books?id=pRWqfsVTAY8C&pg=PA369&lpg=PA369&dq=residual+functions+thermodynamics&source=web&ots=h1kEfOVg4X&sig=u3SAlNM3dmMFYfFkANDhjB47igI [Broken]
    Last edited by a moderator: May 3, 2017
  4. Dec 3, 2007 #3


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    Source: http://imartinez.etsin.upm.es/bk3/c07/Excess functions.htm

    This essentially means that it is a way to "adjust" your model so that it matches the natural phenomenon that you are modeling more closely.

    It's like using a polytropic process with n=1.2 instead of 1.4 to allow for losses due to a gas having thermal losses/gains or doing some amount of work, etc.
    Last edited by a moderator: Apr 23, 2017
  5. Dec 4, 2007 #4


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    A Residual property is a a measure of the deviation from the value that some property would have for an ideal gas at the same conditions.

    For example, if M is the actual value of a thermodynamic property (like the Gibbs free nergy) for a nonideal gas, and Mig is the value the property will have if the gas was ideal at the same T & P, then the residual property MR is defined as,

    MR = M - Mig

    Excess properties are usually used with liquid solutions, or when we want to measure deviations from a nonideal solution. The excess property is similarly defined as

    ME = M - Mid

    ie, the difference between the value of a thermodynamic property of the actual solution and an ideal solution at the same T,P and composition.

    If you want a reference text, try Chapter 11 of "Chemical Engineering Thermodynamics" by Smith, Van Ness and Abbot.
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