Isochores and Heat Capacity of Liquid Water in Terms of the Ion–Molecular Model

Thermodynamics of liquid water in terms of a non-standard approach—the ion–molecular model—is considered. Water is represented as a dense gas of neutral H(2)O molecules and single charged H(3)O(+) and OH(−) ions. The molecules and ions perform thermal collisional motion and interconvert due to ion exchange. The energy-rich process—vibrations of an ion in a hydration shell of molecular dipoles—well known to spectroscopists with its dielectric response at 180 cm(−1) (5 THz), is suggested to be key for water dynamics. Taking into account this ion–molecular oscillator, we compose an equation of state of liquid water to obtain analytical expressions for the isochores and heat capacity.