What does translational energy have to do with entropy change?

[giggidygigg]

I know that the translational energy of gas can be represented by
3/2NkT
where N = number of molecules, k = boltzmann's constant, T = temperature

my textbook says that the change in entropy is
(delta)S = (integral from 1 to 2) dS = (integral from 1 to 2) dU/T + (integral from 1 to 2) PdV/T = NRln(v2/v1)

i know that since U = 0 in an isothermal system, dU/T term gets canceled and the PdV/T term is left, but i don't understand how we get NRln(v2/v1) from it

i also don't know how translational energy comes into place.

much help needed!

 

[mdelisio]

Try using the ideal gas law PV = NRT to put the P/T in terms of V. Hope this helps.