CHE 303 (Winter 2009) __________________
LAST NAME, FIRST
Problem set #9
(1) 1 At 80 o C compounds A and B each have vapor pressures of 700 mmHg. At 80 o C this system forms an azeotrope containing 50 mol % A and exerts a pressure of 960 mmHg. Using Van Laar model, calculate the equilibrium pressure and vapor composition at 80 o containing 25 mol % A .
C over a liquid solution
Ans: y
A
= 0.385, P = 924 mmHg
(2) 1 In the system A-B , activity coefficients can be expressed by ln 
A
= 0.5
x
B
2 and ln 
B
= 0.5
x
A
2
The vapor pressures of A and B at 80 o C are P
A sat = 900 mmHg and P
B sat = 600 mmHg. Is there an azeotrope in this system at 80 o C, and if so, what is the azeotrope pressure and composition?
Ans: x
A
= 0.90547, P = 904 mmHg
(3) 1 At 80 o C compounds A and B each have vapor pressures of 800 mmHg. At this temperature the A-
B system forms an azeotrope containing 50 mol % A at a pressure of 1050 mmHg. Compound A has a heat of vaporization of 8000 cal/mol and B has a heat of vaporization of 10,000 cal/mol.
Estimate the azeotrope composition and pressure at 60 o expressed by
C. The activity coefficients can be ln 
A
= Cx
B
2 and ln 
Ans: x
A
= 0.57865, P = 489.5 mmHg
B
= Cx
A
2
(4) 1 A stream contains 30 mol % toluene, 40 mol % ethylbenzene, and 30 mol % water. Assuming that mixtures of ethylbenzene and toluene obey Raoult’s law and that the hydrocarbons are completely immiscible in water, calculate the temperature and compositions at the bubble point and at the dew point. The total pressure is 1 atm.
Ans: Bubble point, T (K) = 361.62, T (C) = 88.47 y w
= 0.65287, y t
= 0.21751, y e
= 0.03241
Dew point, T (K) = 388.06, T (C) = 114.91 x t
= 0.26565, x e
= 0.73435
(5) 1 At 100 o C nitrobenzene and water are only partially miscible with saturated with saturated liquid compositions at 0.147 mol % nitrobenzene and 91.7 mol % nitrobenzene. At this temperature the vapor pressure of nitrobenzene is 21 mmHg.
(a) Estimate the total pressure and the vapor composition when two liquid phases and a vapor phase are in equilibrium.
(b) To design a stripping column to remove nitrobenzene from dilute aqueous solutions, it is necessary to have vapor-liquid equilibrium data. Estimate the vapor composition in equilibrium with an aqueous solution containing 0.0100 mol % nitrobenzene at a temperature of 100 o estimate the total pressure.
C. Also
Ans: a) y
NB
= 0.0247, P = 778 mmHg b) y
NB
= 0.0017, P = 761 mmHg
1 Kyle, B.G., Chemical and Process Thermodynamics, Prentice Hall, 1999

(6) n-Hexane (1) and ethyl alcohol (2) are put into an evacuated, isothermal container. After equilibrium is established at 75 o C, it is observed that two liquid phases and a vapor phase are in equilibrium. One of the liquid phases contains 9.02 mol % n-hexane. Activity coefficients for this system can be represented by the following equation:
RT ln  i
= 8.163
x j
2
(a) Calculate the equilibrium composition of the coexisting liquid phase.
(b) Calculate the equilibrium pressure and vapor-phase mole fractions.
Data: Vapor pressure equations ( T in o K and P in bar) ln P
1 sat =  4728.98/ T + 13.4643 ln P
2 sat =  3570.58/ T + 10.4575
Ans: a) x
1
II = 0.9098, P = 778 mmHg b) y
1
= 0.4206, P = 1.9656 bar
(7) 1 At equilibrium the following data were taken for the reaction
A (g) = B (g) + C (g)
T ( o C) P (atm)
3.33 y
A
0.200 200
200
300
300
6.00
2.02
5.15
0.333
0.005
0.012 y
B
0.600
0.333
0.4975
0.600 y c
0.200
0.333
0.4975
0.388
Use these data to determine equilibrium mol fraction of A , B , and C that results when A decomposes at 250 o C and 10 atm. Assume ideal gas behavior and  o h rxn
= constant.
Ans: y
A
= 0.11487 y
B
= y c
= 0.44256
(8) 1 For the following gas-phase reaction in equilibrium at 500 o at 10 atm pressure
K it is found that A is 10% dissociated
A (g) = B (g) + C (g)
Assume ideal gas behavior and calculate the percent dissociation of A at 500 o pressure.
K and 1 atm
Ans: 30.3%