CLOSED system, i.e. non-flow processMaximum useful work (Wu)max = Wmax - Watm = Wmax - Po (V2 - V1)where, Po = surrounding or atmospheric pressure, Wmax = the max work that can be extracted when the system is expandingand Watm = Po(V2 - V1) = the work DONE by the system against the surrounding having a flexible BOUNDARY, for a rigid boundary Watm = 0.For a very slow expansion i.e. an isothermal expansion Q = Wmax = P (V2 - V1) as ΔU = 0. (Wu)max = P (V2 - V1) - Po (V2 - V1) = (P - Po) ΔV Calculation:Given, Po = 100 kPa, P = 300 kPa, ΔV = 0.01 m3 from, (Wu)max = (P - Po) ΔV (Wu)max = ( 300-100) x 0.01 = 2kJ For a closed system, maximum useful work is the availability, available energy or exergy.