Standard molar free energy, estimation

From the thermodynamic equilibrium constant, the estimate of the standard molar free energy of ion-pair formation is sanctioned by the well known relationship ... 

This AF° was estimated as follows For the reaction in question, aH may be taken as — 11.3 kcal/mole = —11300 cal/mole (Table V, data of Durell et al., 1962). The total entropy change was estimated as — 2.5 — 16.5 = — 19.0 entropy units. Therefore, AF° = AH - rAS = —11300—300 (—19) =-11300-1-5700=-5600 cal/mole. This molar free-energy change and others designated here by the superscript apply to a standard state with all reactants and products at a concentration of IM, with other conditions as defined above. If the standard state is taken as one in which the hy-dronium ion is at a concentration of 10 , as at pH 7.0, then the superscript will be used. 

Pb(CH3)4 is soluble In absolute ethanol [1, 2], but not in 96% ethanol [3]. It is soluble in ether [1, 2], hydrocarbons, benzene, toluene, and other usual organic solvents [3], but Insoluble in liquid ammonia at —78 C [4]. Solutions of Pb(CH3)4 in C7Hi4-n (components are about equally volatile) are used as standards in atomic absorption spectrometry. Such solutions are stable for more than 6 months In contrast to Pb(C2H5)4 solutions [27]. For a phase equilibrium study of the systems Pb(CH3)4-toluene and Pb(CH3)4-benzene, see [38]. Estimated values of free energies of transfer of Pb(CH3)4 from methanol to water, alcohols, and several other solvents are given in [12, 21]. A solution of 17 to 90% methanol in 0.1 molar acetate buffer is used as a mobile phase for the separation of (CH3)4 nPb(C2H5)n by HPLC [39, 40]. Pb(CH3)4 and acetonitrile form an azeotrope [6]. Pb(CH3)4 is quantitatively extracted from dust samples into cold ammoniacal methanol [24]. The llpophllicity of Pb(CH3)4 is lower than that of Pb(C2H5)4 [41]. 

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