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Ratio PV/RT dieterici's equation

  1. Apr 1, 2014 #1
    Hello
    1. The problem statement, all variables and given/known data
    Determine the ratio PV/RT at the critical point for a fluid which obeys Dieterici’s equation
    p(v-b)=RT exp(-a/RTv)

    2. Relevant equations



    3. The attempt at a solution
    First ofall i don't really understand this notion of critical point.
    I found an equation to find it that is
    (dp/dv)=(d²p/dv²)=0 at constant temperature T
    I don't have any equation in my book so where did this get from ?
    Using it I found that
    V=2nb
    P=a/(4b²e²)
    T=a/4Rb
    And then I don't know what to do

    Thanks
     
    Last edited: Apr 1, 2014
  2. jcsd
  3. Apr 1, 2014 #2
    The critical point is the minimum or maximum value of a function. At this point the gradient (derivative) of the function is 0.

    You are asked to work out the ratio PV / RT .
     
  4. Apr 1, 2014 #3
    The result is supposed to be 2/e² but I get 2n/e² what am i supposed to do with the n ?
     
  5. Apr 1, 2014 #4
    Sometimes the question may ask "per mole".
     
  6. Apr 1, 2014 #5
    Boylanator is correct. The problem statement clearly implies molar V. When did the n come from anyway? It wasn't in the problem formulation.

    Chet
     
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