Pauling's Model and the Thermodynamic Properties of Water

Abstract

A statistical-thermodynamic treatment is given of the model for liquid water recently proposed by Pauling, in terms of a variable distribution of water molecules between the two states—framework water and interstitial water—for which this model provides. This treatment shows that, with simple assumptions, the model can give a satisfactory representation of the P–V–T properties of water over limited ranges of temperature and pressure. The properties (enthalpies and entropies) which are derived for framework and interstitial water, respectively, also seem physically reasonable. The simple model is less successful in representing the heat capacity of water and the partial molal properties of nonpolar solutes. The fact that water is a liquid, however, requires that some molecules be in a ``third state,'' and it is suggested that if this third state is taken into consideration the shortcomings of the simple model can be remedied. Adoption of the Pauling model would seem to have as a corollary the likelihood that the structural ``transition,'' purportedly found in liquid water just above 30°C, may be real.