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

high concentration in the fish, but only a negligible fraction of the benzene is
associated with fish. Such calculations are invaluable, because they establish the
dominant medium into which the chemical is likely to partition, and they even give
approximate concentrations.
5.6.2 The Fugacity Method
We now repeat these calculations using the fugacity concept and replacing C by
Zf. We know that Z will depend on
1. the nature of the solute (i.e., the chemical)
2. the nature of the medium or compartment
3. temperature
4. pressure (but the effect is usually negligible)
5. concentration (but the effect is negligible at low concentrations)
We have developed procedures by which Z values can be estimated for any given
environmental situation. Equilibrium concentrations can then be deduced using f as
a common criterion of equilibrium. We can repeat the previous partitioning example
using the fugacity method and demonstrate the equivalence of the two approaches
as before, but now applying the same fugacity to each phase.
Therefore,
©2001 CRC Press LLC
M = C 1V 1 + C 2V 2 + C 3V 3 + C 4V 4
= Z 1fV 1 + Z 2fV 2 + Z 3fV 3 + Z 4fV 4
= f (V 1Z 1 + V 2Z 2 + V 3Z 3 + V 4Z 4)
f = M/(V 1Z 1 + V 2Z 2 + V 3Z 3 + V 4Z 4)
from which each C can be calculated as Zf, and the amount in each phase m is CV
or VZf.
In general,
Worked Example 5.6
f = M/SV iZ i C i = Z if m i = V iZ if
Using the data in Example 5.5, recalculate the distribution using fugacity and
assuming that Z A is 4 ¥ 10 –4 mol/m 3 Pa.
Z W = Z A/K AW = 0.002
Z S = K SWZ W = 0.03