Relationship between the entropy of transfer of a solute and the thermodynamic functions of mixed solvents

Abstract

Tne entry of a solute into a solvent will affect the interactions between solvent molecules by making, breaking, strengthening or weakening solvent-solvent bonds. In a binary mixed solvent the relative partial molar entropies, si, and excess entropies of mixing, ASE, are related to these interactions. Thus a relationship between the entropy of transfer, A S P , of a solute and these thermodynamic parameters might be expected. A general relationship is developed and successfully applied to the A S P for alkali-metal halides in methanol-water mixtures. The results of this analysis show that, for this system at least, A S P is dominated by the effects of changes in solvent-solvent interactions, in contrast to the enthalpy of transfer, AH?. Combination of the results of this analysis with those previously reported for AH? allows a complete, quantitative explanation of the thermodynamics of solvation in the alkali-metal halides in methanol-water mixtures.Recently' we showed that the enthalpies of transfer, AH?, of a solute in a mixed solvent could be related, quantitatively, to changes in the enthalpies of solvent-solvent bonding in the mixed solvent. This model was found to account satisfactorily for AH? of simple electrolytes in methanol-water mixtures, where they pass through broad maxima as functions of solvent composition, and in acetonitrile-water mixtures, where the (AH?, x,) profiles show sharp minima.In this paper we derive an analogous relationship for the entropy of transfer, ASP, and apply this to data for the alkali-metal halides in methanol-water systems. The variations in the ASP data with solvent composition largely result from the changes in solvent-solvent bonding.The results of this analysis are combined with those from the analysis of the corresponding AH? data and show that the treatment represents satisfactorily the free energies of transfer, AGP.

Thermodynamics of amalgam cells {M-amalgam|MCl2 (m)|AgCl|Ag} (M=Sr, Ba) and primary medium effects in {methanol+water} and {ethanol+water} solvent mixtures

“…The trend of the slope found experimentally for a given electrolyte in the three mixed solvent series is in accordance with FeakinsÕ theory [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37], which considers five contributions to the primary medium effect, each one described by a specific physical property: solvent/ cation and solvent/anion acid-base interactions (described by the GutmannÕs donor or acceptor numbers DN and AN, respectively), ion-dipole interactions (dipole moment, l), ion-dielectric interactions (relative permittivity, e), and induced dipole-induced dipole interactions (polarizability, a). The influence of the first four contributions increases with increasing ion hardness, while the opposite holds for the last contribution.…”

Thermodynamics of the amalgam cells {Cs-amalgam|CsX (m)|AgX|Ag} (X=Cl, Br, I) and primary medium effects in (methanol+water), (acetonitrile+water), and (1,4-dioxane+water) solvent mixtures

“…The slopes of the curves, which are always in the order dioxane ) methanol > acetonitrile, are in accordance with the FeakinsÕ theory [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47], which considers five contributions to the primary medium effect, each one described by the variation (with respect to water) of a specific physical property, namely: relative permittivity e (accounting for ion-dielectric interactions), dipole moment l (accounting for ion-dipole interactions), GutmannÕs donor or acceptor numbers DN and AN (accounting for solvent-cation and solvent-anion acid-base interactions, respectively), and polarisability a (accounting for induced dipole-induced dipole interactions). The influence of the first four contributions increases with increasing ion hardness, while the opposite occurs for the last contribution.…”

Luminescence study on the solvation of Cm(III) in binary aqueous solvent mixtures

“…Preferential solvation in mixed solvents can be described in analogy to complexation reactions, where the preferentially coordinating solvent is considered as complexing ligand [36]. According to the well-established model for solvation of a solute (for a detailed description see [42,43]), the solute occupies a cavity with n neighbouring solvent molecules.…”

“…The model parameters ∆∆H • 12 and (αn + βN) • related to solvent-ion interaction and changes in solvent-solvent bonding in the proximity of Cm(III), respectively, are determined by fitting of the experimental data to an established model of salvation [34][35][36][37][38], rendering valuable thermodynamic information on the interaction of Cm(III) with solvent molecules in aqueous binary mixed media. …”