Valiskó Mónika, Boda Dezső
Department of Physical Chemistry, University of Pannonia , P.O. Box 158, H-8201 Veszprém, Hungary.
J Phys Chem B. 2015 Jan 29;119(4):1546-57. doi: 10.1021/jp509445k. Epub 2015 Jan 12.
We investigate the individual activity coefficients of pure 1:1 and 2:1 electrolytes using our theory that is based on the competition of ion-ion (II) and ion-water (IW) interactions (Vincze et al. J. Chem. Phys. 2010, 133, 154507). The II term is computed from grand canonical Monte Carlo simulations on the basis of the implicit solvent model of electrolytes using hard sphere ions with Pauling radii. The IW term is computed on the basis of Born's treatment of solvation using experimental hydration free energies. The two terms are coupled through the concentration-dependent dielectric constant of the electrolyte. We show that the theory can provide valuable insight into the nonmonotonic concentration dependence of individual activity coefficients. We compare our theoretical predictions against experimental data measured by electrochemical cells containing ion-specific electrodes. We find good agreement for 2:1 electrolytes, while the accuracy is worse for 1:1 systems. This deviation in accuracy is explained by the fact that the two competing terms (II and IW) are much larger in the 2:1 case, resulting in smaller relative errors. The difference of the excess chemical potentials of cations and anions is determined by asymmetries in the properties of the two ions: charge, radius, and hydration free energies.
我们使用基于离子 - 离子（II）和离子 - 水（IW）相互作用竞争的理论（Vincze等人，《化学物理杂志》，2010年，133卷，154507页）来研究纯1:1和2:1电解质的单个活度系数。II项是通过基于使用鲍林半径的硬球离子的电解质隐式溶剂模型的巨正则蒙特卡罗模拟计算得出的。IW项是基于使用实验水化自由能的玻恩溶剂化处理计算得出的。这两项通过电解质浓度依赖的介电常数相互耦合。我们表明该理论可以为单个活度系数的非单调浓度依赖性提供有价值的见解。我们将理论预测结果与使用含离子特异性电极的电化学电池测量的实验数据进行比较。我们发现对于2:1电解质有很好的一致性，而对于1:1体系精度较差。精度上的这种偏差可以解释为在2:1的情况下，两个相互竞争的项（II和IW）要大得多，导致相对误差较小。阳离子和阴离子的过量化学势之差由两种离子性质的不对称性决定：电荷、半径和水化自由能。
