dQ = nCvdT if volume is constant. However, n = pV/RT. What I don't understand is, why are we thinking n as constant when doing the integral? I had two problems that involved this on a test I had today. At first I kept it constant and then changed n. But then I thought, wait... isn't there a T in n? then that T should be in the integral. I understand the point, heat capacity per mole. But mathematically, the T that is in the equation for n should matter, right? dS = dQ / T, if we substitute dQ in that equation we should get 1 / T2 in the integral also. I know I'm wrong however, so if someone could tell me what's wrong?