CHAPTER 12 EQUILIBRIUM CONDITIONS IN MULTICOMPONENT SYSTEMS
12.8 LIQUID–GASEQUILIBRIA 405
Thuscompared to the liquid, the gas phase is richer in the component whose addi-
tion to the liquid at constant temperature causes the total pressure to increase. This
statement is a version ofKonowaloff’s rule.
In some binary liquid–gas systems, the total pressure at constant temperature exhibits
a maximum or minimum at a particular liquid composition. At this composition, dp=dxA
is zero but dpA=dxAis positive. From Eq.12.8.21, we see that at this compositionxA=xB
must equalyA=yB, meaning that the liquid and gas phases have identical mole fraction
compositions. The liquid with this composition is called anazeotrope. The behavior of
systems with azeotropes will be discussed in Sec.13.2.5.
12.8.4 Gas solubility
For the solution process B(g)!B(sln), the general expression for the thermodynamic equi-
librium constant isKDaB(sln)=aB(g).
The activity of B in the gas phase is given byaB(g)DfB=p. If the solute is a nonelec-
trolyte and we choose a standard state based on mole fraction, the activity in the solution is
aB(sln)D x;B (^) x;BxB. The equilibrium constant is then given by