[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.