Download Problem Set 14 Problems

CHEM 331
Physical Chemistry
Fall 2013
Problem Set 14
Problems
1.
The density of Diamond is 3.52 g/cm3 and that of Graphite is 2.25 g/cm3. At 25oC the
Standard Gibbs Free Energy of Formation (Gfo) of Diamond from Graphite is 2.900
kJ/mole. At 25oC what pressure must be applied to bring Diamond and Graphite into
equilibrium? State any approximations made during this calculation.
[Ans. 1.5 x 104 atm]
2.
The melting points of CCl4 at various pressures are given below, along with the Molar
Volume change for Fusion. Calculate Hfus and Sfus at 1 atm and at 4000 atm.
P [atm]
1
1000
2000
5000
7000
t [oC]
-22.6
15.3
48.9
130.8
176.2
V [cm3/mol]
3.97
3.06
2.51
1.52
1.08
[Ans. 1 atm: 2.66 kJ/mol, 10.6 J/K mol and 4000 atm: 2.58 kJ/mol, 6.86 J/K mol]
3.
The Normal Boiling Point of Iodine is 183.0oC; the vapor pressure of the liquid at 116.5oC
is 100 Torr. Hfuso = 15.65 kJ/mole. The vapor pressure of the solid is 1 Torr at 38.7oC.
a) Calculate Hvapo and Svapo.
[Ans. 45.1 kJ/mol, 98.9 J/K mol]
b) Calculate Hsubo.
[Ans. 60.72 kJ/mol]
c) Estimate the Triple Point temperature and pressure.
[Ans. 384K, 81 Torr]
d) Calculate the vapor pressure of the gas over the solid at 25oC.
[Ans. 4.45 x 10-4 atm]
e) Determine Go for:
I2(s)
at 25oC.
[Ans. 19.1 kJ/mol]
I2(g)
f) Calculate Gfo for I2 gas at 298.15K.
[Ans. 19.1kJ/mol]
4.
Benzene and Toluene form nearly Ideal Solutions. At 300K:
PTolo
PBeno
= 32.06 Torr
= 103.01 Torr
a) A liquid mixture is composed of 3 mol Toluene and 2 mol Benzene. If the pressure
over the mixture at 300K is reduced, at what pressure does the first vapor form?
[Ans. 60.5 Torr]
b) What is the composition of the first trace of vapor formed?
[Ans. ytol = 0.32]
c) If the pressure is further reduced, at what pressure does the last trace of liquid
dissapear?
[Ans. 44 Torr]
d) What is the composition of the last trace of liquid?
[Ans. xtol = 0.83]
5.
The vapor pressures of the components in some non-Ideal Binary Liquid-Vapor
Equilibrium systems can be represented by the equations:
P1 = x1aP1*
P2 = x2aP2*
where a is a constant. Show that if the constant a is greater than unity, the total pressure
exhibits a minimum, while if a is less than unity, the total pressure exhibits a maximum.
6.
From the Melting Points of the mixtures of Al and Cu, sketch the Melting-Point curve.
mass % Cu
0
20
40
60
80
100
t [oC]
660
600
540
610
930
1083
Thermodynamic data for these two elements gives:
Element
Cu
Al
Tm [K]
1356
933
Hfuso [kJ/mol]
13.05
10.75
Sketch the Ideal Solubility curves and compare with the experimental curve above. (Both
sketches should be on the same graph and should be quantitative.)