McKay, Donald. "Front matter" Multimedia Environmental Models ...

pseudo-solubilities) in these media and the three partition coefficients are then
discussed in more detail in Section 5.4. Armed with this knowledge we then address
how this “laboratory” information can be applied to environmental media such as
soils and aerosols.
©2001 CRC Press LLC
5.2 PROPERTIES OF PURE SUBSTANCES
For reasons discussed later, it is important to ascertain if the substance of interest
is solid, liquid, or vapor at the environmental temperature. This is obviously done
by comparing this temperature with the melting and boiling points. Figure 5.2 is the
familiar P-T diagram that enables the state of a substance to be determined. Of
particular interest for solids is the supercooled liquid vapor pressure line, shown as
a dashed line. This is the vapor pressure that a solid (such as naphthalene, which
melts at 80°C) would have if it were liquid at 25°C. The reason it is not liquid at
25°C is that naphthalene is able to achieve a lower free energy state by forming a
crystal. Above 80°C, this lower energy state is not available, and the substance
remains liquid. Above the boiling point, the liquid state is abandoned in favor of a
vapor state. It is not possible to measure the supercooled liquid vapor pressure by
direct experiment. It can be calculated as discussed shortly, and it can be measured
Figure 5.2 P-T diagram for a pure substance.