Generalised hydrogen-bonding lattice-fluid theory for thermodynamics of complex systems

A generalised hydrogen-bonding molecular theory of associated systems is proposed based on the nonrandom-lattice-fluid theory and Veytsman statistics. By the two-fluid approximation, configurational Helmholtz free energy was derived from the lattice of the Guggenheim combinatory. The approximate nature of the model makes it possible to unify the classical lattice theory with hydrogen bonding. The model requires only two molecular parameters for a pure fluid. For a binary mixture an additional interaction parameter is needed. Results demonstrated that the model correlates quantitatively the first-order and second-order thermodynamic properties of real fluids. The model is especially relevant to (multi)phase equilibria of systems containing molecularly complex species such as electron donor - acceptors and macromolecules. The model is quantitatively applied to vapour and liquid densities and vapour pressures of pure systems, various vapour - liquid equilibria, and vapour - solid equilibria of associated mixtures with temperature-independent interaction parameters. Also, the model even characterised liquid - liquid equilibria employing temperature-dependent binary interaction parameters well.