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Stuck on integral!

  1. Sep 6, 2008 #1
    1. The problem statement, all variables and given

    integral of : (nRT)/(V-nb)dV from Vi to Vf

    [tex]\int[/tex] [tex]^{Vf}_{Vi}[/tex] (nRT)/(V-nb)dV

    I am really stuck on this one!
    Do you need to move the denominator up first?
    Last edited: Sep 6, 2008
  2. jcsd
  3. Sep 6, 2008 #2
    Assuming that everything except V is a constant for this problem, try the substitution

    u = V -nb
  4. Sep 6, 2008 #3


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    Homework Helper

    You need to tell us which are constants and which are functions of V in this question. Otherwise, the problem becomes very simple when you factor nRT out.
  5. Sep 6, 2008 #4
    Since the integral says "dV" doesn't that mean it only needs to be integrated with respect to the variable V while holding all other variables constant?
  6. Sep 7, 2008 #5
    Assuming everything else is constant.

    factor the nRT out. Let u = V-nb.
    du/dv = 1 if nb is a constant.
    This means that when u differentiate the denominator u get the numerator and its safe to straightaway ln the denominator.

    I think it should be ln|Vf-nb| - ln|Vi-nb|

    i might be wrong though.

    Btw, is it just a practice question or are u doing this for chem? just curious. ;).
  7. Sep 7, 2008 #6
    Also don't forget if you substitute u = V - nb, you must also write the limits of integration in terms of u.
  8. Sep 8, 2008 #7
    I am doing these problems to touch up on my Calc for a class I am taking (physical chem)
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