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Final_Exam_-_December_2013.pdf-Department of Chemistry & Biochemistry Concordia
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Final Exam - December 2013.pdf-Department of Chemi...
Final_Exam_-_December_2013.pdf-Department of Chemistry & Biochemistry Concordia
Final Exam - December 2013.pdf-Depa...
Final_Exam_-_December_2013.pdf-Department of Chemistry & Biochemistry Concordia
Page 4
Department of Chemistry & Biochemistry
Concordia University
Question 3 (5 points).
Consider the phase diagram shown below:
P
c
= critical pressure= 300 atm; T
c
= critical temperature = 200
°
C
(a) Sublimation occurs by release of energy, or by absorption of energy ?
(b) A phase change from region B to region C is known as : sublimation, condensation, freezing,
vaporization or melting ?
(c) At a pressure of 30 atm, the boiling point of this substance is : 50
°
C, -15
°
C, -105
°
C, 0
°
C or
200
°
C?
(d) The area of the graph that represents the liquid phase is : B, C or A?
(e) At standard temperature and pressure (STP), this substance can exist as : a solid only, a liquid
only, a gas only, a solid or a gas?
Question 4 (5 points).
For the reaction :
Fe
2
N (s)
+
3/2
H
2
(g)
2 Fe(s) + NH
3
(g)
the equilibrium ratio of partial pressures

at 700 K and 800 K is 2.165 and 1.083,
respectively.
Assuming that the total pressure is 1.000 bar : calculate K
eq
at 700 K and at 800 K


Page 5
Department of Chemistry & Biochemistry
Concordia University
Question 5 ( 5 points)
(a)
What volume of ethylene glycol (C
2
H
6
O
2
), a non volatile non-electrolyte, must be added to
15,0 L of water to produce an antifreeze solution with a freezing point of
30,0 °C ?
(b)
Also, what is the boiling point of the solution prepared in (a)?
Density of ethylene glycol : 1,11 g/mL; density of water : 1,00 g/mL. Boiling point constant
for water : 0,512 °C-kg / mol; freezing point constant for water : 1,86 °C-kg / mol.
Attempt
only one of the 2 questions below.
If you attempt both questions, only the
first one will be marked.
Question 6 (10 points)
Methylethyl ether, CH
3
-O-C
2
H
5
, (A) and diborane, B
2
H
6
, (B), form a compound which melts
congruently at 133 K. The system exhibits 2 eutectics, one at 25 mol percent B and 123 K, and a
second at 90 mol percent B and 104 K. The melting points of pure A and B are 131 K and 110 K,
respectively. Sketch the phase diagram for this system, and clearly indicate what phases are present
in all the different regions of the graph. Assume negligible solid-solid solubility.
Question 7 (10 points)
The figures below show the experimentally determined phase diagrams for the nearly ideal solution of
hexane (C
6
H
14
) and heptane (C
7
H
16
)
(a) Label the regions of the phase diagrams, as to which phases are present.
(b) For a solution containing 1.0 mol each of hexane and heptanes, estimate the vapour pressure
(at 70
°
C, on the pressure-composition diagram) when (on reduction of the pressure)
vaporization just
begins.
(c) What is the composition of the solution at 70
°
C on the pressure-composition diagram when
one drop of liquid remains?
(d) Estimate the compositions of the liquid and vapor phases in equilibrium in parts b & c above.
(e) Consider another liquid mixture, composed of 3 moles of hexane and 2 moles of heptane. At
85
°
C and 760 torr of pressure (on the temperature-composition diagram), what are the
amounts of substances in the liquid and vapour phases (hint : lever rule)


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