Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Free energy of dissociation

Consider the dissociation of a weak electrolyte such as acetic acid. The dissociation constant is [Pg.312]

According to the remarks made in the previous section the activity coefficient y Ao undissociated acid can probably be taken as [Pg.312]

In the Ostwald treatment of dissociation it was assumed that a is given by A/Aoo, where A is the molar conductivity at the molality m and Aoo is the molar conductivity at infinite dilution. Some values of at 25 worked out on the basis of this supposition, and [Pg.312]

The approximate constancy of the values may be attributed partly to the fact that the concentration of the free ions in the various solutions is very low, so that is close to unity, and partly to the fact that the Ostwald assumption a=A/Aop is probably fairly near to the truth under the same conditions of high dilution of the ions. In general, the Ostwald method gives reasonably satisfactory results for dilute solutions of weak electrolytes for which the dissociation constant is of the order 10 or less. [Pg.313]

In stronger solutions, or in the case of electrolytes which have a higher dissociation constant, y is no longer close to unity. The assumption a=A/A also becomes erroneous. Whenever the con-centration of the ions is appreciable the ions of opposite charge attract each other, with the result that their speed of migration in the electric field is no longer independent of their concentration, as is supposed in the Ostwald treatment. [Pg.313]


From such crude data as are to be found in the literature we can calculate approximate values of the equilibrium constants, and hence of the free energies of dissociation for the various hexaarylethanes. From our quantum-mechanical treatment, on the other hand, we obtain only the heats of dissociation, for which, except in the single case of hexaphenylethane, we have no experimental data. Thus, in order that we may compare our results with those of experiment, we must make the plausible assumption that the entropies of dissociation vary only slightly from ethane to ethane. Then at a given temperature the heats of dissociation run parallel to the free energies and can be used instead of the latter in predicting the relative degrees of dissociation of the different molecules. [Pg.122]

Theoretical considerations show that the free energy of dissociation of an acid in water, and hence the dissociation constant, is governed by the algebraic sum of the free energies for the solution of the undissociated acid in water, for vaporisation of the acid, for the formation of a free proton and an anion from the molecule of acid in the gas phase, and for hydration of the proton and anion. Thus the true acidity, given by the third of these... [Pg.88]

It seems reasonable then to conclude that the heat of formation of NF4+ is greater than 225 kcal./mole and probably less than 260 kcal./ mole a value around 240 kcal./mole seems not unlikely. This implies that dissociation of NF4+ to NF3+ and F should be endothermic by 50 25 kcal./mole, and dissociation to NF2+ + F2 endothermic by 38 24 kcal./ mole. The increase of standard entropy in the latter dissociation is estimated about 45 e.u. this will contribute —13.5 kcal./mole to the standard free energy of dissociation at 300°K. It is thus not unlikely that the ion NF4+ can be prepared and observed in the gas phase by a suitable ion-molecule reaction. [Pg.38]

One example that demonstrates the role of this type of Lewis acid site in surface chemistry is a study of the mechanism of water dissociation over the clean a-Al203(0001) surface by Hass and coworkers [100]. They used the BLYP functional in the CPMD code to allow the free energy of dissociation to be estimated using constrained dynamics [101]. The initial adsorption mode involves the coordination... [Pg.364]

Fig. 4 Energy diagram for the dissociation of the IC of a bola-amphiphile, E hydrophilic end group, AG jss activation free energy of dissociation, AG iss = —AG° free energy of dissociation (reprinted with permission from [31], copyright of the American Chemical Society)... Fig. 4 Energy diagram for the dissociation of the IC of a bola-amphiphile, E hydrophilic end group, AG jss activation free energy of dissociation, AG iss = —AG° free energy of dissociation (reprinted with permission from [31], copyright of the American Chemical Society)...
The relationship in equation 72 indicates that the enthalpic and the entropic contributions to the substituent effect are not independent. Therefore, the assumption that "Og and Og are independent substituent constants accounting for the enthalpic and entropic contributions (22) is not valid. However, for the separation of these contributions, this assumption is not needed, since the enthalpic and entropic contributions to the free energy of dissociation can be obtained experimentally in an independent fashion. In fact, the relationship between the enthalpic and the entropic contributions on one hand with the inductive and resonance effects (which are assumed to be independent) on the other hand can be obtained only by using the relationship between enthalpic and entropic contributions. [Pg.48]

FIGURE 11. Hydrogen-bond interaction of hydroxyarene photoacids (parameter b in equation 18) versus free energy of dissociation of the photoadds in water (from Reference 91)... [Pg.506]

The model assumes the existence of a continuum of binding sites in which the stoichiometric concentration of binding sites with a particular pKa value is functionally related to the pKa value. In other words, the probability of occurrence of a binding site depends on the Gibbs free energy of dissociation of that site. The nature of the hypothesized distribution function is, of course, unknown however, the affinity spectrum technique is specifically designed to numerically estimate that function from observable titration data. [Pg.523]

Table 2 Selected reaction enthalpies and free energies of dissociation reactions of S (n=4, 6, 8, 10) in the gas phase and in SO2 solution at 298 K [in kj mor j. Some equilibria were also assessed using HF (DC=83) or oleum (DC=110) as solvent. Exergonic Gibbs energies of reaction in solution are printed in bold... [Pg.145]

The justification for equation 1 has been presented (3) where AG°3(H20) is the standard free energy of dissociation (homolytic) in aqueous solution and AH°3(gas) is the standard enthalpy of dissociation in the gas phase for an H-X molecule or H-B+ ion. [Pg.167]

Figure 2.20 Example of a linear free-energy correlation. Free energy of benzoylation of substitute anilines versus free energy of dissociation of the aniline. [Data of F.J. Stubbs and C.N. Hinshelwood, J. Chem. Soc., 571 (1949) from K.J. Laidler, Chemical Kinetics, 2nd ed., with permission of McGraw-Hill Book Co., New York, NY, (1965)]. Figure 2.20 Example of a linear free-energy correlation. Free energy of benzoylation of substitute anilines versus free energy of dissociation of the aniline. [Data of F.J. Stubbs and C.N. Hinshelwood, J. Chem. Soc., 571 (1949) from K.J. Laidler, Chemical Kinetics, 2nd ed., with permission of McGraw-Hill Book Co., New York, NY, (1965)].

See other pages where Free energy of dissociation is mentioned: [Pg.516]    [Pg.511]    [Pg.231]    [Pg.36]    [Pg.36]    [Pg.93]    [Pg.107]    [Pg.360]    [Pg.839]    [Pg.432]    [Pg.304]    [Pg.135]    [Pg.17]    [Pg.152]    [Pg.91]    [Pg.92]    [Pg.531]    [Pg.532]    [Pg.93]    [Pg.107]    [Pg.360]    [Pg.298]    [Pg.35]    [Pg.365]    [Pg.337]    [Pg.340]    [Pg.17]    [Pg.570]    [Pg.129]    [Pg.126]    [Pg.183]    [Pg.48]    [Pg.48]    [Pg.171]    [Pg.203]    [Pg.516]    [Pg.236]    [Pg.6162]   


SEARCH



Dissociation free energy

Energy, of dissociation

Standard free energy of dissociation

© 2024 chempedia.info