Temperature dependence of the solubility of non-polar gases in water

An explanation is provided for the experimentally observed temperature depe ndence of the solubility and the solubility minimum of non-polar gases in w ater. The influence of solute size and solute-water attractive interactions on the solubility minimum temperature is investigated. The transfer of a n on-polar solute from the ideal gas into water is divided into two steps: fo rmation of a cavity in water with the size and shape of the solute and inse rtion of the solute in this cavity which is equivalent to 'turning on' solu te-water attractive interactions. This two step process divides the excess chemical potential of the non-polar solute in water into repulsive and attr active contributions, respectively. The reversible work for cavity formatio n is modeled using an information theory model of hydrophobic hydration. At tractive contributions are calculated by modeling the water structure in th e vicinity of non-polar solutes. These models make a direct connection betw een microscopic quantities and macroscopic observables. Moreover, they prov ide an understanding of the peculiar temperature dependences of the hydrati on thermodynamics from properties of pure water; specifically, bulk water d ensity and the water oxygen-oxygen radial distribution function. (C) 1999 E lsevier Science B.V. All rights reserved.