A thermodynamic system is taken through the cycle ABCD as

A thermodynamic system is taken through the cycle ABCD as shown in figure. Heat rejected by the gas during the cyclic process is :

∵ Internal energy is the state function.
∴ In cyclie process; ∆U = 0
According to 1st law of thermodynamics

∆Q = ∆U + W

So heat absorbed
∆Q = W = Area under the curve
= – (2V) (P) = – 2PV
So heat rejected = 2PV