Why PV work in cyclic process is zero?
For a thermodynamic system, in which internal energy is the only type of energy the system may have, as per the law of connservation of energy, we have
Q + W = ΔEint (first law of thermodynamics)
Q is the heat energy transfereed between system and environment. Wis the workdone on (or by ) the system.
ΔEint is the change in internal energy of the system.
for the cyclic process, ΔEint is zero. In cyclic process starting point of the state is same as the ending point of state. Hence change in internal energy is zero.
hence Q+W = 0
it is not pV work alone, which is W as described above is not zero.