Hi guys, I have some questions about this equation: P.V^(gamma) = constant, gamma = C_p / C_v Is it only valid for a adiabatic process, plus ideal gas? I thought it was at the first place, as I saw its derivation uses adiabatic properties(dQ=0) and assumes the gas is ideal (PV=mRT). But when I read my textbook, it doesn't mention anything about adiabatic. It says those processes follow: P.V ^ n = constant (n is another constant) are called 'polytropic'. If the gas is ideal, then the process is isothermal. I become more confuse when I saw 'isothermal', as I thought it should be adiabatic. And, is the equation only valid for a closed system? Last question, is 'TV^(gamma - 1) = constant' valid only for adiabatic process and ideal gas? I like thermodynamics, but I find some parts of it quite confusing, hope someone can clear my doubts. thank you.