Specific surface excess entropy

Besides helping to obtain some feeling for the accuracy of data, the above exercise serves a physical purpose the coefficients A and B are, or are closely related to, the surface excess entropy S and the surface excess specific heat. Regjirding the former, it may be recalled from [l.A.5.3] that... 

Table 1 summarizes the basic relationships that link energy characteristics of excess electrons with the values measured by the aforementioned methods (see also Fig. 1). In the equations given therein, i.e. in Eqs. (5) and (6) w , w , and w denote respectively metal-to-vacuum, metal-to-solution, and solution-to-vacuum photoemission work functions AT is the Volta potential difference for a metal-solution system Eg is the equilibrium potential of the electrode in solvated electron solution and il(RE) is the Fermi level of the reference electrode. Equation (6) is approximate (see above) because the solvated electron entropy has not been taken into consideration. The main error in equating the heat of electron solvation and the activation energy of the thermoemission current for the solvated electron solution is caused by the variation in the solution s surface potential with temperature apparently, here specific adsorption of solvated electrons (or of an alkali metal) on the solution/vapour interface makes major contribution to the surface potential . This error can be probably neglected if measurements are taken in very dilute solutions (<10 mol/1, see ) of the alkali metal. This follows from the dependence measured in between thermoemission current and the concentration of sodium in hexamethylphosphotriamide. 

Thus, cation water clusters favour internal structures in contrast to the surface strucmres favoured by anionic water clusters. This critical difference in the structural preferences of hydrated cation and anion clusters provides important cues for the design of cation- and anion-specific ionophores and receptors. Indeed, we note that most cation receptors have spherical structures, while almost all anion receptors do not have compact spherical structures but have a vacant space around the anion binding site without full coordination (which might be exceptional for the F ion with strong electronegativity for which the excess electron is strongly bound to F due to its small ion radius). However, as the temperature increases, the hydration structure tends to be more spherical due to entropy effects. 

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