| STATISTICAL THERMODYNAMICS OF CHEMICAL EQUILIBRIUM IN NON-IDEAL LIQUIDS: HARD SPHERES, SQUARE-WELL AND COULOMBIC INTERACTIONS Ksenia Peshkina1; 1IHTE RAS, Ekaterinburg, Russian Federation; PAPER: 146/SolutionChemistry/Regular (Oral) SCHEDULED: 17:50/Wed. 30 Nov. 2022/Game ABSTRACT: We present a statistical-thermodynamic description of the diversified influence of pairwise interactions on the position of chemical equilibrium in reactions of various types, such as the dimerization, the formation of heteronuclear molecules, and the complex formation in molten salts with di- and three-valent metals. Models of pair interactions from the simplest potential of hard spheres, through the potential with square well, to the potential of charged hard spheres with different ionic diameters were considered. The dumbbell shape for binary molecules is additionally taken into account and a significant diversity of deviations from ideality were described. The effects of the excluded volume on the shift of chemical equilibrium in binary systems containing the inert solvent have been analyzed [1]. With an increase in the size of the solvent particles, the character of the concentration dependence for the enthalpy of mixing changes from purely endothermic to sign alternative, which has a pronounced exothermic effect at low and medium concentrations. The association in binary hard-sphere liquids was considered taking into account the dumbbell-like shape of heteronuclear molecules [2]. The excess entropy for such a reacting mixture describes the most pronounced ordering with a larger difference in the diameters of monomers, but with a lower their fusion. The influence of attraction between particles on the position of dimerization equilibrium was estimated within the model of square well [3]. An amplification in the attraction between monomers leads to a shift in equilibrium towards the dissociation, while an amplification in the attraction between dimers contributes a shift in equilibrium towards the formation of dimerization products. The inclusion of interparticle attraction, especially between dimeric molecules, leads to an increase in the packing fraction. The evaluation of concentrations of the complex anionic (MX4)2‒ and (MX6)3‒ groups in molten salts have been performed [4, 5]. The calculation according to the ideal mass action law provides a significant overestimation of the concentration of complexes, at that the fraction of complexes is practically equal to the maximum possible (1/2) in the considered temperature range. We will demonstrate that in Coulombic systems there is a temperature threshold above which the complete dissociation of anionic complexes contained in pure and binary molten halides of two- and three- valent metals occurs. Thus, the deviations from ideality in various liquids play an important role can be described by using only a set of parameters characterizing the ratio of particle sizes in a mixture. The report will summarize all the results obtained by us up to date. References: [1] K.G. Peshkina, N.K. Tkachev, J. Mol. Liq. 216 (2016) 856-861. [2] A.G. Davydov, N.K. Tkachev, J. Mol. Liq. 242 (2017) 879-883. [3] A.G. Davydov, N.K. Tkachev, J. Mol. Liq. 275 (2019) 91-99. [4] K.G. Peshkina, N.K. Tkachev, Phys. Chem. Liq. 57 (2019) 768-778. [5] N.K. Tkachev, K.G. Peshkina, Rus. J. Electrochem. 54 (2018) 433-441. |
