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Intensive or extensive variables.

  1. Oct 9, 2006 #1
    In my book:

    But why do the tell me that the need do discribe the extensieve state of a system by using intensive and at least one extensive variable?

    Thanks a lot.
  2. jcsd
  3. Dec 22, 2011 #2
    Hello Bert: you are probably retired from PF by now but the issue might be interesting for others too:
    we take a system consisting of 1 kind of species present (we take helium). internal energy U is an extensive quantity so we need 1+2=3 variables to know it. But U=n(3/2)RT, so here two variables seem to be sufficient, with n extensive and T intensive. In general thermodynamics takes U=U(S,V) which also has only 2 varibles, but for G=G(p,T) 2 would not be enough because both p and T are intensive. ??
    Sorry for the mess.
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