Heat capacities of H2O+H2O2, and H2O+N2H4, binary solutions: Isolation of a singular component forCpof supercooled water

摘要

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 minus;45thinsp;deg;C, an attempt has been made to separate the total heat capacity of water into rsquo;rsquo;anomalousrsquo;rsquo; and rsquo;rsquo;normalrsquo;rsquo; components. The basis for such a separation used here is extrapolation to zero solute content ofCpof binary aqueous solutions from which the low temperature anomalies have disappeared. We have studied two closely related systems based on the second components H2O2and N2H4. The low temperature molarCpisotherms are very unusual. The extrapolations to zero solute ofCpisotherms in the two systems yield similar but not identical rsquo;rsquo;normalrsquo;rsquo; components for pure water. The corresponding alternative sets of rsquo;rsquo;anomalousrsquo;rsquo;Cpcomponents vs temperature data, when besthyphen;fitted to the singular point equationCp(anom)=A(T/Tsminus;1)minus;ggr;, yield within one degree, the sameTsvalue, 226 K, and exponents either side of the classical value of unity. When the value ggr;=1.0 is assigned to the anomalous components of the dilute aqueous H2O2solutions, the best fitTsvalues accurately mirror the behavior of the solution homogeneous nucleation temperatures.