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Homework Help: Sackur-Tetrode expression

  1. Oct 6, 2013 #1
    1. The problem statement, all variables and given/known data
    Write the Sackur-Tetrode expression for the entropy of a monatomic ideal gas as a function of pressure, temperature, and number, S(N,T,P).

    2. Relevant equations
    S = Nk[ln(V/N(4πmU/3Nh2)3/2) + 5/2]
    PV = NkT
    U = (f/2)NkT

    3. The attempt at a solution
    I found that equation for S in my book and also found that f = 3 for monatomic gases. So I used V = NkT/P and U = (3/2)NkT and just put it into the equation for S to get:
    S = Nk[ln(KT/P(2πmT/h2)3/2) + 5/2].

    I just wanted to see if I got this right because sometimes I make stupid mistakes and I didn't want to continue to the next part of the problem if got this part incorrect.
  2. jcsd
  3. Oct 6, 2013 #2


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    Looks pretty good, but I don't think you have enough factors of K in your expression. Also, you might want to combine all factors of K and T to make it look a little nicer.
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