In thermodynamics, the P−V work done is given by w=−∫dVPext. For a system undergoing a particular process, the work done is,
w=−∫dV(RTV−b−aV2)
This equation is applicable to aw=−∫Pext.dV
From van der waal equation of state for one mole gas.(P+aV2)(v−b)=RT
P=[RTV−b−aV2]
Pext=Pgas
W=−∫(RTV−b−aV2)dv
So, process is not applicable only for irreversible process.