A singular thermodynamically consistent temperature at the origin of the anomalous behavior of liquid water

Abstract

The density maximum of water dominates the thermodynamics of the system under ambient conditions, is strongly P-dependent, and disappears at a crossover pressure P[subscript cross] ~ 1.8 kbar. We study this variable across a wide area of the T–P phase diagram. We consider old and new data of both the isothermal compressibility K[subscript T](T, P) and the coefficient of thermal expansion αP(T, P). We observe that KT(T) shows a minimum at T* ~ 315±5 K for all the studied pressures. We find the behavior of αP to also be surprising: all the αP(T) curves measured at different P cross at T*. The experimental data show a “singular and universal expansivity point” at T* ~ 315 K and αP(T*) ≃ 0.44 10[superscript −3] K[superscript −1]. Unlike other water singularities, we find this temperature to be thermodynamically consistent in the relationship connecting the two response functions.