Single-ion entropie

Figure 45. Single ion entropies for various ions in methyl alcohol + water mixtures at 298 K full lines represent idealized dependence and dotted lines show observed dependence (Franks and Reid, 1969).

Tabulated are single-ion entropies of about 110 diatomic and polyatomic ions in water Gibbs energies, enthalpies, and entropies of hydration of monatomic ions at 25 C partial molar volumes of about 120 common ions at 25 C ionic partial molar heat capacities of ions Gibbs energies of transfer of inorganic electrolytes from HjO to 020 and calorimetrically determined enthalpies of solution of salts in H2O and 020. 

Among the papers dealing with potential measurements at isothermal half-cells at normal pressure, such of industrial interest are remarkable, e.g. of the chlorine electrode [41]. Very precise studies at thermocells with the hydrogen electrode, the silver-silver chloride electrode and the silver electrode [42] provided single ion entropies and activation entropies. 

It should be born in mind, however, that the activation parameters calculated refer to the sum of several reactions, whose enthalpy and/or entropy changes may have different signs from those of the decrystalUzation proper. Specifically, the contribution to the activation parameters of the interactions that occur in the solvent system should be taken into account. Consider the energetics of association of the solvated ions with the AGU. We may employ the extra-thermodynamic quantities of transfer of single ions from aprotic to protic solvents as a model for the reaction under consideration. This use is appropriate because recent measurements (using solvatochromic indicators) have indicated that the polarity at the surface of cellulose is akin to that of aliphatic alcohols [99]. Single-ion enthalpies of transfer indicate that Li+ is more efficiently solvated by DMAc than by alcohols, hence by cellulose. That is, the equilibrium shown in Eq. 7 is endothermic ... 

The enthalpies of solution and solubilities reviewed here provide much of the experimental information required in the derivation of single-ion hydration and solvation enthalpies, Gibbs free energies, and entropies for scandium, yttrium, and lanthanide 3+ cations. 

The free energy of solvation of an uncharged species as well as the related enthalpy and entropy quantities are experimentally accessible. The evaluation of the corresponding properties for single ions is only possible with the help of an extra-thermodynamic assumption. This also holds for the free energy of transfer of neutral combinations of ions and the related thermodynamic quantities. 

Alot of information about the free energies of transfer of single ions between pure solvents has been accumulated. Less numerous are determinations in mixed solvents, and the ionic enthalpies of transfer and entropies of transfer as function of mole fraction are known as an exception only. In Table 1 ions and solvent mixtures are listed for which free energies of transfer and some other thermodynamic quantities have been determined. 

A similar trend in the change of the formal or E /2 potentials was observed for solvated cations, for instance for the Eu /Eu couple in different solvents [87, 88]. The analysis of Gibbs energies, entropies and enthalpies of single ion transfer led Gritzner [89] to search for general trends in the interaction of different ions with solvent molecules. The interactions of cations with different solvents were considered, in terms of the Lewis concept, i.e., as a reaction of the acid (cation) with the base (solvent). 

Electroneutrality is required in all solutions thus, it is not possible to measure the properties of a single ion without influence from an ion of opposite charge. By convention, the standard enthalpy of formation and the standard entropy of the... 

Since p = l/(ksT), the term — Br" /(37i) can be identified as the excess entropy per unit volume associated with electrostatic interactions. One may now extract the electrostatic contribution to the single ion activity coeiScient, which is... 

B. G. Cox and A. J. Parker, Solvation of ions. XVII. Free energies, heats, and entropies of transfer of single ions from protic to dipolar aprotic solvents, J. Am. Chem. Soc. 402 (1973). 

In a most recent paper,a new table of absolute single-ion thermodynamic quantities of hydration at 298 K has been presented, based on conventional enthalpies and entropies upon implication of the thermodynamics of water dissociation. From the values of AiydG the Bom radii were calculated from... 

He also showed that the values of the single ion B s could be related to the ionic entropies. 

ELDAR contains data for more than 2000 electrolytes in more than 750 different solvents with a total of 56,000 chemical systems, 15,000 hterature references, 45,730 data tables, and 595,000 data points. ELDAR contains data on physical properties such as densities, dielectric coefficients, thermal expansion, compressibihty, p-V-T data, state diagrams and critical data. The thermodynamic properties include solvation and dilution heats, phase transition values (enthalpies, entropies and Gibbs free energies), phase equilibrium data, solubilities, vapor pressures, solvation data, standard and reference values, activities and activity coefficients, excess values, osmotic coefficients, specific heats, partial molar values and apparent partial molar values. Transport properties such as electrical conductivities, transference numbers, single ion conductivities, viscosities, thermal conductivities, and diffusion coefficients are also included. 

Fig. 4. Solvation free energy and entropy from simulations compared with experimental values, (a) and (b) Comparison between experimental and calculated solvation free energies using different parameter sets for anions (a) and cations (b). (c) and (d) Comparison between experimental and calculated solvation entropies using different parameter sets for anions (c) and cations (d). Plotted are the simulated solvation free energies/entropies versus the experimental solvation free energies/entropies. The experimental solvation free energies and entropies are taken from Marcus/ leading to the solid lines. The dashed Knes show the experimental single-ion properties shifted in such a way that (i) the shifts of an anion and a cation cancel each other, and (ii) the Dang chloride ion exactly reproduces the experimental data.

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