Water’s Unusual Thermodynamics in the Realm of Physical Chemistry

Abstract

While it is known since the early work by Edsall, Frank and Evans, Kauzmann, and others that the thermodynamics of solvation of nonpolar solutes in water is unusual and has implications for the thermodynamics of protein folding, only recently have its connections with the unusual temperature dependence of the density of solvent water been illuminated. Such density behavior is, in turn, one of the manifestations of a nonstandard thermodynamic pattern contemplating a second, liquid–liquid critical point at conditions of temperature and pressure at which water exists as a deeply supercooled liquid. Recent experimental and computational work unambiguously points toward the existence of such a critical point, thereby providing concrete answers to the questions posed by the 1976 pioneering experiments by Speedy and Angell and the associated “liquid–liquid transition hypothesis” posited in 1992 by Stanley and co-workers. Challenges of this phenomenology to the branch of Statistical Mechanics remain.

Self-diffusion and shear viscosity for the TIP4P/Ice water model

“…3 Indeed, the conversion between highly ordered tetrahedral water arrangements and disordered domains of high density are in the origin of most of water's anomalies. 4 This equilibrium, which persists in room temperature water, can be traced back to thermodynamic anomalies of metastable, supercooled water. 5 Therefore, the properties of supercooled water have been extensively studied, including the fragile-to-strong transition, 6,7 and the preservation of the Stokes-Einstein relation.…”