Free energies and entropies of transfer of hydrobromic and hydroiodic acids from water to t-butyl alcohol + water mixtures from electromotive force measurements at different temperatures (5—35°C)

Abstract

Free energies, AGtO and entropies, AS," of transfer of hydrobromic and hydroiodic acids from water to t-butyl alcohol+ water mixtures containing 10, 20, 30 and 50 % t-butyl alchol by weight have been evaluated using the corresponding values of the standard potentials, EO, of silver-silver bromide and silver-silver iodide electrodes in these solvents obtained from electromotive force measurements at seven different temperatures ranging from 5 to 35°C performed on the cell Pt, H,(g, 1 atm)lHX(m), solventlAg-AgX, where X = Br or I. These and the corresponding values for HCl obtained from Eo data given in literature were used to evaluate AGf for individual ions by the " extrapolation procedure ". In contrast with other aqueous organic solvents, humps or kinks in the AG,O against composition profiles occur at water-rich compositions reflecting the strong structural characteristics of this solvent system in that region. The variation of entropies of transfer with composition has been interpreted in terms of marked structure-promotion of water and consequent ion-dehydration at small concentrations of t-butyl alcohol and of the formation of alcohol-water complexes at somewhat higher contents of t-butyl alcohol. The irregular order Br-> I-> C1-in water-rich regions for the entropy profiles is suggested to be due to the formation of charge-transfer complexes of the iodide ion with t-butyl alcohol.

Thermodynamic transfer study of various metal chlorides from water to formamide and dimethylformamide by EMF measurements

“…Therefore metal ion interactions with solvent molecules could be investigated by measuring the EMF. To investigate and interpret these interactions further, we preferred to calculate the standard thermodynamic functions [23] ( G • , H • and S • ) and standard transfer thermodynamic parameters [24] ( G • tr , H • tr and S • tr ) from one solvent (W) to other solvents (FD and DMF). Their computed values are reported in Tables 3 and 4 respectively.…”

Chemical Transfer Energetics of the −CH2− Group: A Possible Probe for the Solvent Effect on Hydrophobic Hydration and the 3D-Structuredness of Solvents

“…p K c sp values and free energies of solution Δ G ° s on molar scale of all the salts at five temperatures in water and aqueous alkanols and ACN were computed using the relations where s is the observed saturated solubility in mol dm -3 listed in Table and y ± is the mean molar activity coefficient of the salts as computed by the use of the extended Debye−Huckel equation . Values of density ( d s ) and dielectric constant (ε s ) are taken from the literature. − Ion-size parameters of the ions are taken to be 0.3 nm . The estimated uncertainties in Δ G ° s are about ±0.025 kJ mol -1 .…”

“…As in previous works, , the estimated uncertainties in Δ G ° t and Δ S ° t are about ±0.05 kJ mol -1 and ±2 J K -1 mol -1 , respectively. Δ G ° t (i) values can be divided into cavity, electrostatic, and chemical contributions where Δ G ° t,cav (i) is the difference in free energy change involved to create cavities for the ion in water and aquo-cosolvents from scaled particle theory (SPT), ,,22a, and Δ G ° t,el (i) is the electrostatic term associated chiefly with a Born-type interaction 26 and ion−dipole interaction term . Corresponding ion-induced dipole (i−d) and ion-quadrupolar (i−q) interaction terms are likely to be negligibly small 19,28 and are not included in Δ G ° t,el (i).…”

“… a For computing Δ P ° t,cav (i), Δ P ° t,B (i), and Δ G ° t,i - d (i) values, the required diameter of the solvent constituents and the value of dipole moment of aquo-alkanols and the ACN are taken as given in ref a and the required diameter of the ionic species are obtained from ref a, a, and 31. b Δ G ° t and T Δ S ° t values of Ag + in aqueous ACN are obtained from ref b. …”

Thermodynamic determination of solvation potentials of divalent metal chlorides (MCl2) in iso–dielectric media by EMF measurements

“…To investigate and interpret the ion-solvent interactions, we preferred to calculate the standard thermodynamic functions [26] (DG°, DH°, and DS°), and also the standard transfer thermodynamic parameters [27] (DG tr , DH tr , and DS tr ) from water to isodielectric media. The standard cell potential (E°) was calculated first from the measured cell EMF for the following cell reaction:…”