Standard Gibbs energy of solution

Conventional standard Gibbs energy of solution and the solvation Gibbs energy... 

In Section 6.9, we saw that the standard free energies of formation of aqueous ions can often be determined from E° values. Worked example 7.9 provides an illustration of the use of reduction potential data in a calculation of a standard Gibbs energy of solution of an ionic salt. 

The determination of the standard Gibbs energies of transfer and their importance for potential differences at the boundary between two immiscible electrolyte solutions are described in Sections 3.2.7 and 3.2.8. 

The derivation for equilibrium between a solution and a gaseous phase is based on the Henry law constant kiy defined on page 5. The standard Gibbs energy of the transfer of HC1 from a solution into water is... 

The first term on the right-hand side is in this ideal solution approach given by the standard Gibbs energy of oxidation... 

It is apparent that the deviation from Nemstian behaviour depends on the activity of the determinand and anion B in the studied solution. It decreases with increasing magnitude of the sum of the standard Gibbs energies of transfer of ions J and B " from water into the membrane phase. The effect of the interfering anion is suppressed by increasing the concentration of the ion-exchanger ion in the membrane. 

As an example, consider phenol as the solute and water and toluene as two solvents. The parameters for phenol are A = 5.7, A = -12.9, A = -18.3, and A5 = 0.0091, whereas Aq is unspecified, but a negative quantity. With the solvent parameters from Tables 2.1 and 2.3, the standard Gibbs energy of solvation of phenol in water becomes Aq + 3.39, and in toluene Ao -1- 4.11 kJ mol". It is seen that As i,Gb is lower in water than in toluene, so that the transfer of phenol from water to toluene entails an increase in AjoItGb. The consequence of this is that phenol prefers water over toluene, since work would be required to make this transfer. It should be remembered that the standard Gibbs energies of solvation refer to the state of infinite dilution of the solute (solute-solute... 

Solubility products can be derived indirectly from standard electrode potentials and other thermochemical data, and directly from tabulated standard Gibbs energies of formation, AfG°, of the ions in aqueous solution [12]. Thus, the use of... 

Table 2.3 contains the standard Gibbs energies of formation and the standard enthalpies of formation of a selection of main group cations at 25 °C. They refer to the formation of 1 mol dm- solutions of the cations from their elements and are relative to the values for the hydrated proton taken as zero. 

The data required for method II are the measurable quantities AGf°[ij] and, if Kn is not 0, AHmn, Tmn, and Cps[n] and an extrapolated quantity Cp[n], To make use of available data, the standard Gibbs energy of formation can be expressed in terms of the standard enthalpy and entropy of formation. The advantage of this formulation is that thermodynamic information for unstable or metastable systems is required only for the elements (i.e., Cp[n]), for which a better estimate can usually be made. This data base contains no explicit liquid-solution properties. 

Klaning UK, Sehested K, Holcman J (1985) Standard Gibbs energy of formation of the hydroxyl radical in aqueous solution. Rate constants for reaction CI02 + O3 <=> 03 + CIO2. J Phys Chem 89 760-763... 

Mavrovouniotis, M.L. 1990. Group contributions for estimating standard Gibbs energies of formation of biochemical compounds in aqueous solution. Biotechnol. Bioeng. 36, 1070-1082. 

The standard Gibbs energy of formation of ions in solution... 

We consider only aqueous solutions here, but the methods used are applicable to any solvent system. The standard Gibbs energy of formation of a strong electrolyte dissolved in water is obtained according to Equation (11.28). In such solutions the ions are considered as the species and we are concerned with the thermodynamic functions of the ions rather than the component itself. We express the chemical potential of the electrolyte, considered to be MVtAv, in its standard state as... 

The compilations by Wagman et al. and Robie et al. are quite extensive, including many solids as well as ionic solutes in aqueous solution. Since a compound may be written as the product of a chemical reaction that involves only chemical elements as reactants, and since pP for an element is equal to zero, pP for a compound can be considered to be a special example of ArG° for a reaction that forms the compound from its constituent chemical elements. Thus pP values also are termed standard Gibbs energies of formation and given the symbol AfG°. In addition to p° (or AfG°) values, Wagman et al. and Robie et al. list H° and S° for many substances. These Standard-State thermodynamic properties are related to ArH° and ArS° in Eq. 1.42 15... 

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