In previous work, we have developed a close-packed lattice model for binary solutions of chain-like molecules. As a continuation, considering the effect of volume change, we present here a new molecular-thermodynamic model based on lattice fluid theory. The resulting equation of state shows good performance in describing thermodynamic properties such as pVT behavior, vapor pressure and liquid volume of pure normal fluids. Equation-of-state parameters are obtained by correlation of experimental data. The model is extended to calculate vapor-liquid equilibria of binary mixtures with only one binary interaction parameter. Comparison between the present model and other theories is also presented. (c) 2008 Elsevier B.V. All rights reserved.