AbstractThis paper addresses the effect in chain liquids on thermodynamic behavior of a large charge in the strength of local interactions on mixing. We classified real systems according to the ability of the Flory equation of state (FES) theory to prodict the excess volume. The FES theory enables reliable estimates provided the mixture is nearly athermal and the pure components obey the Flory equation of state. These requirements arise from Flory's approximations for the lattice part of the configuration integral,ZL, and the cell part,ZC, respectively. We revisedZLwithout adding adjustable parameters by the quasichemical perturbation method to account for local ordering in the mixture because of a large change in the strength of binary interactions on mixing. The modification improves the predictions of the thermodynamic functions for systems where Flory'sZLis inadequate.