Activity coefficients of individual ions in LaCl$_{3}$ from the II+IW theory

Abstract

We investigate the individual activity coefficients of ions in LaCl$_{3}$ using our theory that is based on the competition of ion-ion (II) and ion-water (IW) interactions (Vincze et al., J. Chem. Phys. 133, 154507, 2010). 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. This agreement is remarkable considering the facts that (i) the result is the balance of two terms that are large in absolute value (up to $20 kT$) but opposite in sign, and (ii) that our model does not contain any adjustable parameter. All the parameters used in the model are taken from experiments: concentration dependent dielectric constant, hydration free energies, Pauling radii.