Multicomponent Equilibrium Thermodynamics - Elements of Environmental Engineering: Thermodynamics and Kinetics - page 73

FIGURE 3.7 Three-dimensional ice lattice structure.

on the special structural features of water that are of relevance in understanding the
hydration of neutral and polar compounds.

3.4.3.1 Special Structural Features of Water

Water is an inorganic compound. It is the only inorganic compound that exists on
earth in all three physical forms, namely, gas, liquid, and solid. It is a remarkable
solvent and there is practically no compound on earth that is insoluble in water. Large
molecules such as proteins are hydrated with water molecules. Small molecules such
as helium and argon (rare gases) have low solubilities in water. Ionic compounds (e.g.,
NaCl) are highly soluble in water. Particulate and suspended materials in water exist
in the atmosphere as aerosols, fog, and mist. In spite of its ubiquitous nature in our
environment, the structure of water is far from being completely resolved.
Water displays anomalous properties. It expands in volume on freezing unlike the
other compounds. It exists over a wide range of temperature as a liquid that indicates
that long-range intermolecular forces are dominant. That the molar enthalpy of fusion
(5.98 kJ/mol) is only 15% of the molar enthalpy of vaporization (40.5 kJ/mol) is
indicative of the fact that water retains much of its ordered ice-like structure even as
a liquid, which disappears only when it is boiled. The melting point, boiling point,
and the enthalpy of vaporization are unexpectedly high for a compound of such a
low molecular weight. Not that these high values are unusual, but they are mostly
exhibited by metallic and ionic crystals. Although ice is less dense than liquid water,
the isothermal compressibility of liquid water is remarkably low, indicating that the