Contributions to the isothermal compressibility coefficient of water near the temperature of 42 °C

Abstract

Using modern databases, the behavior of the isothermal compressibility coefficient −(∂V/∂P)T = VβT of water in the liquid state near its specific temperature of θ = 42.2 ± 0.2 °C was analyzed. The applicability of the principle of corresponding states in a wide range of thermodynamic parameters of water has been confirmed, excluding the area of water anomalies. The following anomalies of the physical–chemical properties of water were observed: (a) the temperature of θ = 42.2 ± 0.2 °C was found at which the entropy contribution to the isothermal compressibility coefficient of water changed its sign and became positive below this temperature; (b) the temperature of θ = 28.8 ± 0.2 °C was found at which the energy contribution to the isothermal compressibility coefficient of water changed its sign and became negative below this temperature; and (c) the temperature of θ = 17.6 ± 0.2 °C was found at which the energy and entropy contributions to the isothermal compressibility coefficient of water were equal. The entropy contribution to the isothermal compressibility coefficient, according to the two-structure model of water, can be associated with the existence of an “expanded” low-density water structure of hydrogen bonds, the role of which increases with decreasing temperature. We associate the energy contribution to the isothermal compressibility coefficient with the “collapsed” high-density water structure of hydrogen bonds, the role of which in the field of thermodynamic anomalies of water decreases as the temperature decreases.