Heat capacities of H2O+H2O2, and H2O+N2H4, binary solutions: Isolation of a singular component for <i>C</i> <i>p</i> of supercooled water

Abstract

In an effort to examine further the suggestion that anomalies in the properties of supercooled water reflect the approach to a thermodynamic singularity in the vicinity of −45 °C, an attempt has been made to separate the total heat capacity of water into ’’anomalous’’ and ’’normal’’ components. The basis for such a separation used here is extrapolation to zero solute content of Cp of binary aqueous solutions from which the low temperature anomalies have disappeared. We have studied two closely related systems based on the second components H2O2 and N2H4. The low temperature molar Cp isotherms are very unusual. The extrapolations to zero solute of Cp isotherms in the two systems yield similar but not identical ’’normal’’ components for pure water. The corresponding alternative sets of ’’anomalous’’ Cp components vs temperature data, when best-fitted to the singular point equation Cp(anom)=A (T/Ts−1)−γ, yield within one degree, the same Ts value, 226 K, and exponents either side of the classical value of unity. When the value γ=1.0 is assigned to the anomalous components of the dilute aqueous H2O2 solutions, the best fit Ts values accurately mirror the behavior of the solution homogeneous nucleation temperatures.