# New Considerations Around the Singular Water Temperature Explaining the Anomalous Behavior of Liquid Phase

## TL;DR

The paper explores how water's unique hydrogen bonding leads to unusual behavior at a specific temperature around 315 K, linked to its structural phases.

## Contribution

The study proposes a universal temperature where water's thermodynamic properties change, explained by the coexistence of two liquid phases.

## Key findings

- A singular temperature T* ≃ 315±5 K is identified where water's isothermal compressibility and expansivity show anomalies.
- The behavior at T* is attributed to the coexistence of low-density and high-density liquid phases of water.
- The average intermolecular distance supports the existence of two distinct liquid phases in supercooled water.

## Abstract

The water thermodynamics is characterized by polydispersity, which determines its structural and dynamic properties. This is due to the specifics of its characteristic bond: the hydrogen bond (HB). The isobars of the two fundamental thermodynamic functions, the isothermal compressibility (KT(P.T)) and the isobaric expansivity (αP(P,T)), show the presence of a temperature T*≃315±5 K where both have a singular behavior. In this work, by carefully considering the thermal properties of the isobars of density ρ, specific heat CP and the self-diffusion DS, we suggest the universality characteristics of this temperature. In addition, by analyzing the average intermolecular distance dOO, in the same area of the P-T phase diagram, we demonstrate that such realities are due in the supercooled liquid state to the ratio between its two characteristic phases: the low-density liquid (LDL due to HB) and the HDL (which entirely characterizes the remaining parts of the phase diagram).