Affinity to equilibrium

Because at equilibrium there is no flow of components, the rate constants of forward reaction (k+) and reverse reaction (/ ) must counterbalance. Moreover, because affinity to equilibrium is zero, activity product Q must be equivalent to equilibrium constant K. For a generic reaction j at equilibrium, we have... 

Degree of Saturation of Condensed Phases and Affinity to Equilibrium in Heterogeneous Systems... 

Recalling now the concept of thermodynamic affinity (section 2.12), we can, in a similar way, define an affinity to equilibrium as... 

The chemical reaction (I) caimot come to equilibrium directly it can come to equilibrium only if the two electrodes are coimected so that electrons can flow. One can use this feature to detennine the affinity (or the AG) of reaction (I) by detennining the affinity of reaction (II) which balances it. 

The term in parenthesis, as we saw in Eq. (8), expresses the affinity of the reaction towards equilibrium. In marked contrast to Eq. (8), however, is the term 6i, which describes the fraction of free sites available for reaction. Thus even if the rate constants and the affinity towards equilibrium are high, the rate of the process may still be low if there are insufficient free sites, if the surface is blocked such that 6 0. 

It should be mentioned that one can detect two types of equilibrium in the model of charge transfer in the absorbate - adsorbent system (i) complete transition of chemisorbed particles into the charged form and (ii) flattening of Fermi level of adsorbent and energy level of chemisorbed particles. The former type takes place in the case of substantially low concentration of adsorbed particles characterized by high affinity to electron compared to the work function of semiconductor (for acceptor adsorbates) or small value of ionization potential (for donor adsorbates). The latter type can take place for sufficiently large concentration of chemisorbed particles. 

The relationship between fluctuation and dissipation is reminiscent of the reciprocal Onsager relations that link affinity to flux. The two relationships become identical under Onsager s regression hypothesis which states that the decay of a spontaneous fluctuation in an equilibrium system is indistinguishable from the approach of an undisturbed non-equilibrium system to equilibrium. The conclusion important for statistics, is that the relaxation of macroscopic non-equilibrium disturbances is governed by the same (linear) laws as the regression of spontaneous microscopic fluctuations of an equilibrium system. In the specific example discussed above, the energy fluctuations of a system in contact with a heat bath at temperature T,... 

Holmes, Frederic L. "From Elective Affinities to Chemical Equilibrium Berthollet s Law of Mass Action." Chymia 8 (1962) 105146. 

THL.IO. I. Prigogine, P. Outer, and C. Herbo, Affinity and reaction rate close to equilibrium, J. Phys. Colloid Chem. 52, 321-331 (1948). 

The antisera which were collected at ca. 100 days were first characterized for STXOL affinity (33). Equilibrium dialysis (34) gives a good measure of both antibody-to-hapten affinity ( gj useful range for RIA development 10 L/mole) and antibody... 

Thus, the sorption of chemicals on the surface of the solid matrix may become important even for substances with medium or even small solid-fluid equilibrium distribution coefficients. For the case of strongly sorbing chemicals only a tiny fraction of the chemical actually remains in the fluid. As diffusion on solids is so small that it usually can be neglected, only the chemical in the fluid phase is available for diffusive transport. Thus, the diffusivity of the total (fluid and sorbed) chemical, the effective diffusivity DieS, may be several orders of magnitude smaller than diffusivity of a nonsorbing chemical. We expect that the fraction which is not directly available for diffusion increases with the chemical s affinity to the sorbed phase. Therefore, the effective diffusivity must be inversely related to the solid-fluid distribution coefficient of the chemical and to the concentration of surface sites per fluid volume. 

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