Physical Chemistry , 1st ed.

Solution

Refer to Figure 7.17. Using the tie lines to connect the vapor composition

for each liquid phase composition, we ultimately find ourselves at a compo-

sition consisting ofx 1 0. Therefore, the pure component 2 is our ultimate

product.

As an additional example, what is the expected outcome if the solution had

an initial mole fraction x 1 of 0.1? Is your conclusion the same as the conclu-

sion for the additional example in Example 7.7?

If deviations from ideality are large enough, then two liquids won’t even

make a solution at certain mole fractions: they will be immiscible.As long as

there is enough of each component to establish an equilibrium with a vapor

phase in the system, the pressure-composition phase diagram will look some-

thing like Figure 7.18. Between points A and B, we are implying that the two

182 CHAPTER 7 Equilibria in Multiple-Component Systems

T(BP 2 )

T(BP 1 )

Temperature

0.5

x 1 , y 1

0.0 1.0

Final composition

of distillate:

pure component 2

Initial composition

of liquid phase

Figure 7.17 See Example 7.8. If one starts with a liquid having the composition indicated, the

ultimate product will be one of the pure components.

p* 2

p* 1

Pressure

0.5

x 1

0.0 A 1.0B

Region of immiscibility

Total pressure

Partial pressure of component 2

Partial pressure of component 1

Figure 7.18 For very nonideal solutions, there may be ranges of immiscibility. In those ranges,

the vapor composition will not change. Here, the region between points A and B is a region of

immiscibility. The vapor pressure is constant in that range.