Aqueous solutions. Part 3.—Thermal and acoustic characteristics of water

Abstract

The relaxational functions for the expansivity of water have been derived using the relaxational compressibility functions obtained previously. The expansivity can be interpreted in terms of a bond-breaking model whereby the anomalous component is associated with the 1-bonded and 0-bonded OH groups. The relaxational heat capacities have been estimated from the corresponding compressibilities and expansivities.

On the basis of evidence from acoustic data, which indicated the possibility of a thermal relaxation, the anomalous heat capacity has been resolved into two components C_py1 and C_py2. C_py1 values follow a critical law and are similar to those obtained from extrapolations of binary solution and high-pressure data. C_py2 is associated with the thermal relaxation.

Overall the results show that the 1-bonded and 0-bonded equilibrium is probably the critical factor underlying the anomalous properties of water, and that the activation mechanism for this equilibrium could be a quantal one. That is, a time delay in the redistribution of energy between vibrational and rotational (or purely rotational) degrees of freedom could govern the hydrogen-bond equilibrium. The ‘dispersion’ hydrogen-bond energy, δH, identified previously, is of the right order to represent the quantum energy involved.