Structural Characteristics of Concentrated Aqueous Solutions of Lithium Bromide under Extreme Conditions, Evaluated by the Method of Integral Equations

Abstract

The influence of temperature (T 298-623 K) at constant pressure (P 200 bar) on the structure of aqueous solutions LiBr:nH2O (n = 15, 8, 4) was studied using the method of integral equations. In the less concentrated solutions, heating results in disappearance of the tetrahedral ordering of solvent molecules; in the more concentrated soltion, this ordering is lacking even at 298 K. In the systems LiBr:15H2O and LiBr:8H2O, with heating, the hydrogen bonding and the coordinating power of the cation get considerably weakened, the amount of contact ion pairs grows, and the amount of hydration-separated ion pairs decreases. On heating, the H bonds between the anion and water molecules of its first coordination sphere are largely ruptured. At the same time, the structuring of the LiBr:4H2O solution under extreme conditions has certain specific features: with increasing temperature, the intermolecular hydrogen bonding becomes stronger, and the amount of hydration-separated ion pairs increases.