A. G. Davydov, N. K. Tkachev
ABSTRACT
Chemical equilibria in nonideal systems are considered, namely, in associating fluids, where pair interactions between monomers and dimers are described by the potential of a square well with different depth and width. The association is limited to the dimerization stage, in which the molecule is considered as a sphere of compound diameter, drawn around overlapping hard spheres of small radius, that correspond to monomers. It is shown that the attractive part of the intermolecular interaction may be manifested in the form of alternating deviations of the chemical equilibrium from ideality. The various influence of attractive and repulsive forces acting between monomers and dimers on the position of associative equilibrium in different temperature intervals is illustrated. The strengthening of the attraction between the monomers and (or) the weakening between the associates contributes to the shift of the equilibrium toward dissociation. The effects of density change at the variation of the width and depth of square wells in the associated mixture were analyzed. The increase in the packing fraction is most pronounced with an increase in the width of the square well, describing the attraction between the dimers for the cases of small bond lengths.
KEYWORDS:
association, chemical equilibrium, intermolecular attraction, excluded volume, dimers, hard spheres, pair potentials, square well, thermodynamics of the liquid phase.