Concise Physical Chemistry

c09 JWBS043-Rogers September 13, 2010 11:26 Printer Name: Yet to Come

142 THE PHASE RULE

(b) What is the effect of a decrease in atmospheric pressure on the freezing and

boiling points of benzene?

(c) Describe the behavior of a system that is carried along a horizontal line above

the critical point of the phase diagram for water (Fig. 9.3).

(d) Describe the behavior of a system that is carried along a horizontal line below

the critical point, but above the triple point of the phase diagram for water

(Fig. 9.3).

(e) Describe the behavior of a system that is carried along a horizontal line below

the triple point of the phase diagram for benzene (solid lines Fig. 9.3).

Problem 9.3

Describe the behavior of the system with a mole fraction 0.75 well above the dome-

shaped coexistence curve in Fig. 9.9 as the temperature is slowly decreased.

Problem 9.4

Describe the behavior of the system with a mole fraction 0.25 well above the coex-

istence curve in Fig. 9.11 as the temperature is slowly decreased.

Problem 9.5

The vapor pressure of liquid benzene is given by

lnPvap=−

4110

T

+ 18. 33

in the approximate location of the triple point (McQuarrie and Simon, 1997). The

sublimation pressure of solid benzene is given by

lnPsub=−

5319

T

+ 22. 67

What is the triple point for benzene?

Problem 9.6

Sketch a binary phase diagram resembling Fig. 9.10.

(a) Locate the points corresponding to pure components. Call them components

X and Y.

(b) Locate a point corresponding to an equimolar mixture of X and Y.

(c) Locate a point corresponding to a mixture of 20% X and 80% Y.

(d) Locate the point corresponding to the compound X 2 Y.