A thermodynamic system is taken through the cycle ABCD. as shown in figure. Total heat rejected by the gas during the cycle is

∴ΔW=− Area of rectangle ABCD=-P2V=-2PVAccording to first law of thermodynamicsΔQ=Δu+ΔW  or ΔQ=ΔW( As ΔU=0)i.e., heat supplied to the system is equal to the work doneSo heat absorbed, ΔQ=ΔW=−2PV∴  Heat rejected by the gas = 2PV