Two cylinders of equal volume are connected by a valve. We are given the pressure for one of them, and then told to find the final equilibrium pressure after the valve is opened. Adiabatic process may be assumed. I know the solution, but not sure why its that way... initially, I tried PiV1^gamma = Pf(V1+V2)^gamma. But the correct method is: PiV1^gamma =PfV1^gamma+PfV2^gamma. Someone please tell me how the latter is valid. It seems to me that it violates the basic formula PV^gamma = constant.