Free energy of ionization

Free energies of ionization are calculated from equilib rium constants according to the relationship... 

FIGURE 19 3 The free energies of ionization of ethanol and acetic acid in water The electrostatic po tential maps of ethoxide and acetate ion show the concentration of negative charge in ethoxide versus dispersal of charge in ac etate The color ranges are equal in both models to al low direct comparison... 

Calculate AS° for ionization of each compound. Comment on the contribution of AH° and AS° to the free energy of ionization. Test the data for linear fiee-energy correlations. Are the linear free-energy correlations dominated by entropy or enthalpy terms ... 

The standard free energy of formation of a gaseous metal ion, AGj (M+, g), can be viewed as the sum of the standard free energy of sublimation, AGj (M , g), and the free energy of ionization, AG j. The standard entropy of a monatomic gas is very nearly equal to the standard entropy of its corresponding monatomic gaseous... 

State-of-the-art calorimetry allows the accurate determination of enthalpies and free energies of ionization with micromolar amounts of weak acids and bases. The acidic pKs as well as the neutralization enthalpies of imidazole and pyrazole have been determined by calorimetry. 

Table 3.14 Free Energies of Ionization and Solvation of Amines and Ammonium Ions...

The electrostatic free energy of ionization, as calculated from (11) with ZA = +1 and ZB = — 1, is always positive. The quantity d In D/dT is always negative because thermal motion overcomes the orientation of dipoles in an electric field therefore A8el is always negative. The values of D, AFel, AHa, and ASel for several representative solvents are given in Table 8 (Frost and Pearson, 1961). Comparison with the data in... 

Figure 3.13. The Stern-Volmer quenching constant Ko obtained in Ref. 53 versus the free energy of ionization AG . The open circles are the data borrowed from another work [106], The free-energy dependence shown by the solid line represents the theoretical expectation of Rehm and Weller deduced from their original approach to the simplest reaction mechanism of quenching [53], (From Ref. 107.)...

The importance of solvent effects can be extracted from correlations of half-wave potentials determined by CV or polarographic methods with other measures of oxidizability, especially gas-phase free energies of ionization and ionization potentials. Within a series of unsubstituted metallocenes that differ only by the metal, the oxidation potentials of the compounds in solution and their gas-phase free energies of ionization vary directly (Fig. 17),154, 60 indicating that the effect of solvent is consistent from one metallocene to another. 

Fig. 17. Correlation of the gas-phase free energies of ionization and oxidation potentials for unsubstituted metallocenes. The vlP for all compounds are from Ref. 154 the sources of the Ex and values are as follows [CoCp2] and [CrCp J. Refs. 198. 199 [NiCps] and [FeCpi]. Refs. 198. 200 [OsCp2l. Refs. 201. 202.

From the pKa values, the following sequence of 2-substituted 4-thiazolidinones with respect to the degree of acidity are 5 > 2 > 3.186 The opening of the thiazolidinone ring leads to an increase in acidity, but does not affect the activity sequence of the substituents.186 The acidity of a series of substituted 5-benzylidene-2,4-thiazoIidinediones has been investigated the entropy, enthalpy, and free energy of ionization have been calculated.187 Potentiometric determination of the tautomeric equilibrium constants of various 4-thiazolidinones has been reported.188... 

Equation (15) shows that AGa° must be combined with the difference in the free energies of ionization of reactants and products in this case. To have a negative AGb°, the difference in carbocationic stabilization (4 G r - A G ) must not exceed the energy gain by conversion of a ttcc into a [Pg.81]

The values (listed in Tables X-XV) of the standard Gibbs free energies of ionization, AG°, for both processes increase with the increasing organic content of the solvent mixture. This trend is consistent with the effect of the lowered dielectric constant of the mixed solvent and it is caused by the increase of the electrostatic free energies of the ions produced in the dissociation process. 

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