1. The problem statement, all variables and given/known data We have a cylindrical container filled with a gas: the container has an upper compartment with 2 moles of this gas, and another compartment below with 1 mole of the same gas, separated by a diathermic boundary, and also has an adiabatic mobile plunger over the upper compartment. The lower compartment has a kind of grinder (I don't know how to translate it, sorry) which can do work on it. A picture of the container: [Broken] The initial pressure in both compartments and in the outside is [itex]p_0[/itex], and the temperature is [itex]T_0[/itex]. The heat capacity at constant pressure is [itex]C_p = 3R[/itex]. Now imagine the "grinder" does 500J of work at the lower compartment. What will be the final [itex](p,V,T)[/itex] state of the two gases? 2. Relevant equations The equation of state of the gas is [itex] p(V-b) = nRT [/itex] Also, the internal energy (as deduced in a previous part of the problem) is [itex] U = 2nRT [/itex] 3. The attempt at a solution It is clear that the upper compartment remains at constant pressure and that the temperature at both parts of the tank will be the same along the expansion of the upper gas. The work done by the grinder is in form of heat, I think. But i don't know how to proceed. Any clues will be appreciated. Thanks!