Can anyone help me with this, please? 1. 1 mol of an ideal gas is compressed slowly and isothermally at 400 K in a piston-cylinder arrangement. Initial pressure = 100 kPa, final pressure 1000 kPa. The system is surrounded by a resevoir at 300 K such that heat exchange can take place between the piston-cylinder arrangement and the resevoir. System is isolated, so no heat exchange with outside world. Calculate the entropy change of the gas, resevoir and universe if: i. the piston is frictionless. I'm stuck trying to do the entropy change for the gas. If I manage to do it, I should be able to do the rest. I know delta S = INT dQ/T (haven't used tex before) Also, from the 1st law: delta U = Qin + Won For an isothermal change, delta U = 0 (as U depends on T only) => Qin = -Won => Qin = INT P dV I'm not sure where to go from there, cos I can't put dQ = P dV in the integral above, can I (then substitute P = nRT/V, obviously)?