CONDUCTIMETRIC DETERMINATION OF THERMODYNAMIC PAIRING CONSTANTS FOR SYMMETRICAL ELECTROLYTES
CONDUCTIMETRIC DETERMINATION OF THERMODYNAMIC PAIRING CONSTANTS FOR SYMMETRICAL ELECTROLYTES
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DOI：
10.1073/pnas.77.1.34
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发表时间：
1980-01-01
期刊：
影响因子：
--
通讯作者：
FUOSS, RM
中科院分区：
文献类型：
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作者：
FUOSS, RM
早期的理论的电解质电导进行审查，所有这些，除了阿鲁修斯-奥斯特瓦尔德理论，是基于物理模型。他们的理论未能描述强电解质的导电性，因为它没有包括长程力对迁移率的影响（当时没有想到）。热力学推导与模型无关;应用于自由离子和非导电配对离子之间的假设平衡A++ B-Δ A+ B-，热力学配对常数Kaalsap/（a±）2，配对离子（活度=ap）和自由离子（活度=a±）之间的自由能差ΔG等于（-RTlnKa）。换算成摩尔浓度标度，Ka=（1000 ρ/M）[1 - γ）/cy 2（y±）2]。其中ρ是分子量为M的溶剂的密度，电解质的顺式化学计量浓度（mol/L），γ是以未成对离子形式存在的溶质的分数，以及±是它们的活度系数。相应的电导函数Λ = Λ（c;Λ0，R，△G）包含三个参数：Λ0，极限等效电导;R，离子共球半径之和; ΔG。溴化铯和氯化锂在水/二氧六环混合物和碱金属卤化物在水中的电导数据进行分析，以确定这些参数。讨论了R和Δ G值与盐和溶剂性质的关系。
Earlier theories of electrolytic conductance are reviewed; all of these, with the exception of the Arrhenius-Ostwald theory, are based on physical models. Their theory failed to describe the conductance of strong electrolytes because it did not include the effects (then unsuspected) of long-range forces on mobility. Thermodynamic derivations are independent of model; applied to the postulated equilibrium A++ B-⇄ A+B-between free ions and nonconducting paired ions, the thermodynamic pairing constantKaequalsap/(a±)2, and ΔG, the difference in free energy between paired ions (activity =ap) and free ions (activity =a±), equals (-RTlnKa). Converting to the molarity scale,Ka= (1000 ρ/M)[1 - γ)/cy2(y±)2]. Here ρ is the density of the solvent of molecular weightM,cis stoichiometric concentration of electrolyte (mol/liter), γ is the fraction of solute present as unpaired ions, andy±is their activity coefficient. The corresponding conductance function Λ = Λ(c;Λ0,R,△G)involves three parameters: Λ0, the limiting equivalent conductance;R, the sum of the radii of the cospheres of the ions; and ΔG. Conductance data for cesium bromide and for lithium chloride in water/dioxane mixtures and for the alkali halides in water are analyzed to determine these parameters. Correlations between the values found forRand ΔGand properties characteristic of salt and solvent are then discussed.