SCHOOL OF CHEMISTRY & PHYSICS
UNIVERSITY OF KWAZULU-NATAL, PIETERMARITZBURG CAMPUS
MODULE CODE : PHYSICAL CHEMISTRY CHEM330P1
JUNE 2015 MAIN EXAMINATION
DURATION: 3 HOURS
TOTAL MARKS: 100
External Examiner:
Internal Examiners:
Professor E. Iwuoha (University of the Western Cape)
Professor I. Nikolayenko (UKZN)
(Module Coordinator)
Dr D. Reddy (UKZN)
Dr B. Xulu (UKZN)
Instructions:
This paper consists of 9 pages, including Appendix A, a data sheet, and the
periodic table of elements.
Please see that you have them all.
The use of non-programmable electronic calculators is permitted.
The paper is subdivided into three sections. Please, answer questions from
EACH SECTION in a SEPARATE booklet.
Answer ALL questions.
Students are requested, in their own interests to write legibly
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University of KwaZulu-Natal, School of Chemistry and Physics, Pietermaritzburg Campus
June 2015 Main Examination Session, CHEM330P1 Physical Chemistry
Section A:
Question One
(a)
(i) Give the definition and explain the physical meaning of the isobaric coefficient of
thermal expansion, , and the isothermal compressibility, .
(3)
(ii) Estimate the change in volume of liquid water when 1.00 dm3 sample of it is
heated through 5 K at ambient conditions (SATP). For water,   2.1×10-4 K-1 .
(2)
(iii) Estimate the value of  for the water vapour at 25 C and 760 Torr, an average
atmospheric pressure in Durban. Clearly indicate any assumptions made.
(2)
(iv) At SATP conditions, for water   49.6×10-6 atm-1 , and CP ,m  75.29 J K -1 mol-1 .
What is CV,m for liquid water?
(3)
(b)
(i) Give the definition of the chemical potential of a substance.
(1)
(ii) Briefly explain the role of chemical potentials in equilibrium thermodynamics.
(2)
(c)
Draw a sketch of a real one-component phase diagram of your choice with more than
three phases. Clearly label all phase areas, boundaries, and non-variant points.
(7)
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University of KwaZulu-Natal, School of Chemistry and Physics, Pietermaritzburg Campus
June 2015 Main Examination Session, CHEM330P1 Physical Chemistry
Question Two
(a)
Give verbal and mathematical definition of the Raoult law and the Henry law; briefly
explain the difference between the two.
(5)
(b)
At 50 C the vapour pressure of pure CS2 is 854 Torr. When 2.0 g of sulfur were
dissolved in 100 g of CS2 the vapour pressure dropped to 848.9 Torr. Determine the
formula of the sulfur molecule. Clearly state any assumptions made.
(5)
(c)
A monolayer of CO molecules (effective area 0.13 nm 2) is adsorbed on the surface of
1.00 g of an Fe/Al2O3 catalyst at -191.5 °C, the boiling point of liquid carbon
monoxide. Upon warming, when desorbed, the carbon monoxide gas occupies
4.25 cm3 volume at 0 °C and 1.00 bar. What is the surface area of the catalyst?
(4)
(d)
A certain solid sample adsorbs 0.44 mg of CO when the pressure of the gas is
26.0 kPa and the temperature is 300 K. The mass of the gas adsorbed when the
pressure is 3.0 kPa and the temperature is 300 K is 0.19 mg. The Langmuir isotherm
is known to describe the adsorption in this case. Find the fractional coverage of the
sorbent surface at 10.0 kPa pressure.
(6)
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University of KwaZulu-Natal, School of Chemistry and Physics, Pietermaritzburg Campus
June 2015 Main Examination Session, CHEM330P1 Physical Chemistry
Section B:
Question Three
(a)
Consider the following second-order autocatalytic reaction:
A
k2
B + ...
Assuming a small amount of B is present initially, obtain an expression for it
concentration, [B], at any time t in terms of the initial concentrations of A and B (i.e.
[A]0, [B]0).
(12)
(b)
Consider the following the following reaction mechanism in which X is a reactive
intermediate and Y and Z are the final products of the reaction:
k1
A + B
X + A
k-1
k2
X
Y
k3
X + B
(i)
Z
Apply the steady-state treatment to the reactive intermediate, X, and obtain
an expression for the rate of formation of Z.
(3)
(ii)
How would the expression for the rate of formation of Z change if A was
present in excess?
(2)
(iii)
Using the rate of formation of Y, show that if A is present in excess the first
reaction is rate-controlling.
(3)
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University of KwaZulu-Natal, School of Chemistry and Physics, Pietermaritzburg Campus
June 2015 Main Examination Session, CHEM330P1 Physical Chemistry
Question Four
(a)
Give the expression for the Gibbs phase rule and explain the meaning of each of the
terms appearing in it.
(3)
(b) A binary solution of A and B with xB = 0.5783 has a boiling point temperature of
96 C. At this temperature the vapour pressures of pure A and B are 110.1 kPa and
94.93 kPa, respectively.
(i)
Determine, through suitable calculations, whether this solution is ideal.
(4)
(ii)
What is the composition (the mole fraction of B) of the vapour above the
solution?
(2)
(c)
Thermal analysis of the Sn-Mg binary system gave the following cooling curve data
for mixtures of different overall compositions:
Composition / mol% Mg
0
10
40
67
80
90
100
Temperature of break / °C
–
–
600
–
610
610
–
250
200
200
800
580
580
650
Temperature of halt / °C
(i)
Using Figure 1 in the Appendix (which must be submitted with the answer
booklet for this section), sketch and label the simplest temperature-composition
phase diagram that is consistent with these data.
(7)
(ii)
Clearly identify the compound formed and suggest a reasonable formula for it.
(2)
(iii)
Explain what is mean by the term “eutectic”.
(2)
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University of KwaZulu-Natal, School of Chemistry and Physics, Pietermaritzburg Campus
June 2015 Main Examination Session, CHEM330P1 Physical Chemistry
Section C:
Question Five
(a)
Briefly describe the phenomenon known as “ultraviolet-catastrophe”.
(4)
(b)
Define the following terms:
(i)
Quantization
(ii)
Normalization
(2)
(c)
Indicate whether the following statement is true or false, and provide a clear
explanation for your answer.
“For the particle in a box the ground state wavefunction has n = 0.”
If the statement is false, give the correct answer.
(2)
(d)
For a quantum particle in a one-dimensional box, calculate the probability of it being
confined in the range 0.5a ≤ x ≤ 0.75a, where a is the width of the box, in the first
excited state. Recall that the wave function for the particle in a box is given by:
12
2
 n 
 n ( x)    sin 
x .
a
 a 
(6)
(e)
The stretching mode of NO molecule gives rise to an absorption at 1903 cm-1 in the
IR spectrum. What is the force constant, k, of the bond?
(4)
(f)
State which of these molecules will give a pure rotational spectrum and provide an
explanation for your answer: HCl or Cl2?
(2)
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University of KwaZulu-Natal, School of Chemistry and Physics, Pietermaritzburg Campus
June 2015 Main Examination Session, CHEM330P1 Physical Chemistry
Appendix A
Surname: ……………………………..
Figure 1.
Student Number: …………………
Temperature-composition phase diagram for Question Four.
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