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Entropy of solvation

Although the right-hand sides of Eqs. (8.27) and (8.28) are the same, the former applies to the mixture (subscript mix), while the latter applies to the mixing process (subscript m). The fact that these are identical emphasizes that in Eq. (8.27) we have calculated only that part of the total entropy of the mixture which arises from the mixing process itself. This is called the configurational entropy and is our only concern in mixing problems. The possibility that this mixing may involve other entropy effects—such as an entropy of solvation-is postponed until Sec. 8.12. [Pg.512]

An ion s solvated state can be described in two ways (1) in terms of the energy effects the heat, work, = -AG and entropy, of solvation... [Pg.107]

Table 7 illustrates that the entropies of solvation are smaller in water than in DMSO. This can be attributed to the fact that the former has a more pronounced liquid structure. [Pg.80]

Whether obtained from an actual experimentally feasible process or from a thought process, As i Gg, which is obtained from Eq. (2.9) by re-arrangement, pertains to the solvation of the solute and expresses the totality of the solute-solvent interactions. It is a thermodynamic function of state, and so are its derivatives with respect to the temperature (the standard molar entropy of solvation) or pressure. This means that it is immaterial how the process is carried out, and only the initial state (the ideal gaseous solute B and the pure liquid solvent) and the final state (the dilute solution of B in the liquid) must be specified. [Pg.49]

Solvation, the interaction of a solute with the solvent, makes an important negative contribution to the entropy of a solution. Solvation can take the form of hydrogen bonding to donor or acceptor groups on the solute, or of a looser clustering of solvent molecules oriented around the solute (fig. 2.3). In general, the entropy of solvation by water be-... [Pg.34]

It is noteworthy that enthalpy depends mainly on electronic interactions, while entropy depends mainly on trans-lation and rotation solvation affects both enthalpy and entropy. Enthalpies and entropies of solvation usually tend to oppose each other. For charged species, the more negative (favorable) the enthalpy of solvation, the more negative (unfavorable) the entropy of solvation. [Pg.34]

Why do enthalpies and entropies of solvation tend to negate one another ... [Pg.45]

Hickel B, Sehested K (1985) Activation energy for the reaction H + OH" —> eaq. Kinetic determination of the enthalpy and entropy of solvation of the hydrated electron. J Phys Chem 89 5271-5274 Hoffman MZ, Hayon E (1973) Pulse radiolysis study of sulfhydryl compounds in aqueous solution. J Phys Chem 77 990-996... [Pg.85]

The reactions with which we are mostly concerned in chemistry take place in solution rather than in the gas phase. The majority of them moreover involve reactants, products, or transition states carrying electric charges. In such cases the entropies of solvation are extremely large, and these entropies cannot be estimated at present. This immediately rules out any possibility of estimating absolute values of equilibrium or rate constants for reactions of this kind. If we are concerned with absolute calculations of rates and equilibria, we must confine ourselves either to gas-phase reactions, or to reactions of non-polar type. Even here we will usually be forced to make estimates of entropies that are of dubious significance chemical theory has not yet progressed to a point where problems of this kind can usefully be discussed. [Pg.66]

An alternative procedure to gain deeper insight into the physico-chemical basis of solvation consists of the partitioning of AGsoi into its enthalpic, A//soi, and en-tropic, A.S(o, components. Taken together, these quantities represent a substantial reservoir of information about the interactions between solute and solvent molecules. Moreover, these quantities are state functions and can be rigorously derived by using standard thermodynamic relationships, as noted in Eqs. 4-2 and 4-3. Finally, the availability of experimentally measured data for the enthalpy and entropy of solvation makes it possible to calibrate the reliability of theoretical models to predict those thermodynamic quantities. [Pg.104]

Several methods involve a study of the properties of solutions in equilibrium and are hence reasonably described as thermodynamic. These methods usually involve thermal measurements, as with the heat and entropy of solvation. Partial molar volume, compressibility, ionic activity, and dielectric measurements can make contributions to solvation studies and are in this group. [Pg.50]

In Section 2.13, it was shown how it is possible to obtain the entropy of solvation for an electrolyte, but that left open the separation into the individual entropies of solvation for each ion. [Pg.110]

The entropy of solvation values reflect solvational structure near an ion. The following discussion of models that are more in agreement with the experimental values of solvational entropies follows the seminal treatment due to Bockris and Saluja in 1982. Models for the region near an ion are shown in Fig. 2.37. The entropy of hydration from the model with no SB region was 170 to 250 J mol" lower (more negative) than the experimental values, and was therefore not pursued further. [Pg.126]

Is There a Connection between the Entropy of Solvation and the Heats of Hydration ... [Pg.138]

If any three of the four reactions can be measured or calculated, the fourth can be found by completing the cycle. It has been possible to estimate the solvation effects of many ions by comparing similar measurements on a number of different compounds. Naturally, the entropy of solvation also needs to be included as part of the thermodynamics of solubility. [Pg.222]

Estimation of the entropy of solvation requires calculation of the entropy of the ion in the gas phase. For a monoatomic ion, the main contribution to the entropy comes from its translational energy. Simple ions formed from the main group elements have the electronic structure of an inert gas and therefore do not have an electronic contribution to the entropy. On the other hand, ions formed from transition metals may have an electronic contribution to the gas phase entropy, which depends on the electronic configuration of the ion s ground state and of any other electronic states which are close in energy to the ground state. The translational entropy is given by the Sackur-Tetrode equation, which is obtained from the solution of the SWE for a particle in a box (see section 2.2)... [Pg.101]

Table 3.4 Experimental Value and Estimates According to the Born Model and Mean Spherical Approximation for the Gibbs Energy and Entropy of Solvation of the Alkali Metal Cations and Halide Anions at 25°C... Table 3.4 Experimental Value and Estimates According to the Born Model and Mean Spherical Approximation for the Gibbs Energy and Entropy of Solvation of the Alkali Metal Cations and Halide Anions at 25°C...
The entropy of solvation is obtained from the temperature derivative of AjGj [16]. Recognizing that X depends on temperature, the resulting expression is... [Pg.108]

The above empirical model can be extended to estimation of the entropy of solvation. When equation (3.5.13) is differentiated with respect to temperature, one must consider the temperature variation of 8s and /dd as well as the temperature dependence of Sj. However, the number of data points is too few to determine all the temperature coefficients which arise. [Pg.111]

Estimate the entropy of solvation of K in NM given that the temperature coefficient of the permittivity is —0.161 K. Use both the Born model and the MSA. Compare these with the experimental estimate of — 181 JK mol at 25°C. What are the contributions to long-range interactions which depend on dEs/dr, and local interactions which depend on dSs/dr, in this estimate ... [Pg.145]


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See also in sourсe #XX -- [ Pg.104 ]

See also in sourсe #XX -- [ Pg.547 , Pg.548 , Pg.549 , Pg.550 , Pg.554 ]




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