1. The problem statement, all variables and given/known data Using the expression for the entropy change of an ideal gas when the volume and temperature change and TV[itex]\gamma-1[/itex] = constant, show explicitly that the change in entropy is zero for a quasi-static adiabatic expansion from state V1T1 to state V2T2. 2. Relevant equations TV[itex]\gamma-1[/itex] = constant dS = dQr / T 3. The attempt at a solution My idea was to use T1V1[itex]\gamma-1[/itex] = T2V2[itex]\gamma-1[/itex] and solve for T in terms of V and substitute in to the second equation. I couldn't figure it out from there, so my question is is my idea of what to do fundamentally wrong, or is my calculation once i set up the problem wrong?