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Homework Help: Internal energy, thermodynamics

  1. Feb 13, 2008 #1
    [SOLVED] Internal energy, thermodynamics

    1. The problem statement, all variables and given/known data
    I have the equation for the internal energy:

    U = (f/2) * N * k * T, where f is the degrees of freedom, N is the number of molecules, k is Bolzmann's constant and T is the temperature in Kelvin.

    This can be written as U = (f/2)*p*V using the ideal gas law. Differentiating this I get:

    delta U = (f/2)*(delta_p*V + p*delta_V).

    In this equation, I know what delta_p and delta_V are, but what about V and p? Are they the initial or final states?

    Thanks in advance.
     
  2. jcsd
  3. Feb 13, 2008 #2
    V and P are just what they were before you differentiated the expression.

    you get delta_U as a function of P, V, Delta_p and delta_U. V and p are NOT the initial or final values.
     
  4. Feb 14, 2008 #3
    I'm sorry, but I don't understand what you mean.

    V and p are not the final or initial values? If not, what are they then?
     
  5. Feb 14, 2008 #4
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