A simple model for the anomalous excess thermodynamic properties of water is described which, without postulation of molecular species, leads to a "two-state" thermodynamic description as zeroth-order approximation. The model, which is consistent with the common notion that water is best regarded as a disrupted tetrahedral network, involves the concept of elementary configurational excitations of an initially totally connected random network ground-state quasi-lattice. The zeroth-order equations allow a better description of the configuration heat capacity of water and its temperature dependence than those achieved by "mixture model" two-state equations. The model also appears consistent with proton magnetic resonance chemical shift data and with the broad-band aspects of infrared and Raman spectral findings. With an additional postulate concerning the cooperative nature of the flow process, but without additional parameters, the non-Arrhenius temperature dependence of viscosity and other relaxation processes is correctly described and the negative "volume of activation" is accounted for. A glass transition near 159°K is predicted. It is suggested that first-order corrections to the model, which would take into account the cooperative aspects of hydrogen bonding in water suggested by recent quantum-mechanical calculations on static groups, effect mainly the low temperature properties. Their inclusion may lead to an account of the accelerating negative thermal expansion coefficient observed for highly supercooled water.
|Original language||English (US)|
|Number of pages||8|
|Journal||Journal of physical chemistry|
|State||Published - Dec 1 1971|
ASJC Scopus subject areas
- Physical and Theoretical Chemistry