If Q, E and W denote respectively the heat added, change in...

Key Idea : In a cyclic process, system is not isolated from the surroundings. In a cyclic process, a system starts from one point and ends at the same point. In this case, the change in the internal energy must again be zero and therefore the thermal energy added to the system must equal the work done during the cycle. That is, in a cyclic process. $\Delta$U=0 $\text{ or }$E=0