Thermodynamics salt effects

The dissociation constants are thermodynamic constants, independent of ionic strength. Equation (8-33), which was derived from (8-30), is, therefore, identical in its form, and its salt effect, with Eq. (8-31). Therefore, salt effects cannot be used to distinguish between Eqs. (8-30) and (8-31). Another way to express this is that if kinetically equivalent forms can be written, it is not possible to determine, on the... 

La Mar (150) and Walker (156) have found a thermodynamic cis effect in the formation of hemichrome salts [Fe(TRP)L2]Cl (->-[27]) according to equilibrium (77) which was studied by 1H-NMR and optical spectroscopy for L = l-Melm (Table 22). As the electron-donating power of the para-phenyl-substituent of the porphyrin increases, the total formation constant, /J2, increases. This is because the product of the reaction contains a positively charged center which is stabilized by electron-donating groups. As a Hammet relation exists, the mesomeric part of the electronic transmission is also operative, and hence dative porphyrin-to-metal tr-bonding seems to be involved. 

Salt effects in kinetics are usually classified as primary or secondary, but there is much more to the subject than these special effects. The theoretical treatment of the primary salt effect leans heavily upon the transition state theory and the Debye-Hii ckel limiting law for activity coefficients. For a thermodynamic equilibrium constant one should strictly use activities a instead of concentrations (indicated by brackets). 

For comparison with these data, the types of salt effects that have been observed for model protein and polypeptide systems that achieve true thermodynamic equilibrium in solution can be summarized into three classes ... 

A review is presented of techniques for the correlation and prediction of vapor-liquid equilibrium data in systems consisting of two volatile components and a salt dissolved in the liquid phase, and for the testing of such data for thermodynamic consistency. The complex interactions comprising salt effect in systems which in effect consist of a concentrated electrolyte in a mixed solvent composed of two liquid components, one or both of which may be polar, are discussed. The difficulties inherent in their characterization and quantitative treatment are described. Attempts to correlate, predict, and test data for thermodynamic consistency in such systems are reviewed under the following headings correlation at fixed liquid composition, extension to entire liquid composition range, prediction from pure-component properties, use of correlations based on the Gibbs-Duhem equation, and the recent special binary approach. 

The use of a dissolved salt in place of a liquid component as the separating agent in extractive distillation has strong advantages in certain systems with respect to both increased separation efficiency and reduced energy requirements. A principal reason why such a technique has not undergone more intensive development or seen more than specialized industrial use is that the solution thermodynamics of salt effect in vapor-liquid equilibrium are complex, and are still not well understood. However, even small amounts of certain salts present in the liquid phase of certain systems can exert profound effects on equilibrium vapor composition, hence on relative volatility, and on azeotropic behavior. Also extractive and azeotropic distillation is not the only important application for the effects of salts on vapor-liquid equilibrium while used as examples, other potential applications of equal importance exist as well. 

From thermodynamic considerations and after a sequence of simplifying assumptions has been applied, including those of constant temperature and pressure, an equation for the salt effect in vapor-liquid equilibria under conditions of constant mixed-solvent composition has been derived (22,23). The equation, in its simplest form, reduces to... 

Alcohols exhibit a bifunctional nature in aqueous solution. On the one hand, there exists a hydrophobic hydrocarbon group which resists aqueous solvation on the other, there is the hydrophilic hydroxyl group which interacts intimately with the water molecules. Franks and Ives (30, 31) have reviewed experimentation and theoretical treatises on the structure of water, the structure of liquid alcohols, and the thermodynamic, spectroscopic, dielectric, and solvent properties and P-V-T relationships of alcohol-water mixtures. Sada et al. (27) reviewed, in particular, the salt effects of electrolytes in alcohol-water systems and discussed the various correlations of the salt effect applied to these systems. Inorganic salts were used almost universally in these salt effect studies. 

This ionization constatil in terms of activities is called the true or thermodynamic ionization constant. It docs not differ too much from the K in Eq. (14) for sufficiently low ionic strengths. The two differ more markedly for appreciable ionic strengths. Nuw suppose a salt with no common ion is added to the solution. The ionic strength of the solution will be increased. This increase in ionic strength causes a decrease in the activity coefficients of the ions except in very concentrated solutions. Thus for K of Eq. (18) to stay constant the concentrations of the ions must increase to offset the decrease in their activity coefficients. The ammonia must therefore increase in ionization and K as defined by Eq. (14) must increase. This is known as a salt effect. 

Spectrophotometric experiments, however, do not provide straightforward evidence for the existence of small amounts of americium hydroxypolymers. In order to compare the literature data with one another and with our data, they are transformed to thermodynamic data at I = 0 according to Baes and Mesmer (1), using the salt effect constants assessed by them. These data are given in parentheses in Table I. The first hydrolysis constants given in the literature differ from one another considerably. For lanthanide ions, log Bi values are reported from 3.7 to 6.3 (1), which are distinctly lower than that of americium shown in Table I. 

Then simulations of salt solutions in contact with ice were performed. In general, melting temperature decreased and freezing was observed at -15". Also, the time needed to freeze the sample grew dramatically with increasing salt concentration. These are direct demonstrations of the kinetic and thermodynamic antifreeze effects of the added salt at the molecular level. 

The kinetic measurements have confirmed that the epoxidation of COLs with PAs is a second order reaction. The reaction rate depends on the concentration of the COL and PA as well on the nature of solvent [5-8] and its proton donor properties [7]. The reaction rate is influenced by the dielectric constant of the reaction medium, although there has been no salt effect and no autocatalysis observed [7, 9, 10]. The kinetic and thermodynamic data are in accordance with the mechanism of the COLs epoxidation with PAs which was suggested by Bartlett [11]. The reaction rate of the epoxidation of COLs with PAs is strongly af-... 

BUR Burba, C.M., Carter, S.M., Meyer, K.J., and Rice, C.V., Salt effects on poly(A/-isopropylaciylamide) phase transition thermodynamics from NMR spectroscopy, J. Phys. Chem. B, 112,10399, 2008. 

Such salt effects are of practical importance in stagemise separation processes and in pollution abatement. Certain salts increase the solubility by more than an order of. magnitude (salting-in), and also change the solvent selectivity for various solutes others decrease the solubility (salting-out) (4, 6, 7, 10) Partial molal properties of the dissolved gas are also profoundly affected by the addition of salt. Thermodynamic properties of gas-electrolyte solution are also an important consideration in the design and operation of fuel cells, where mass transfer of... 

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