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PCH602S - PHYSICAL CHEMISTRY - 1ST OPP - JUNE 2023 |
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nAm I BIA un IVERSITY
OF SCIEn CE Ano TECHn OLOGY
FACULTYOF HEALTH, NATURAL RESOURCESAND APPLIEDSCIENCES
SCHOOL OF NATURAL AND APPLIED SCIENCES
DEPARTMENT OF BIOLOGY, CHEMISTRY AND PHYSICS
QUALIFICATION: BACHELOROF SCIENCE
QUALIFICATION CODE: 07BOSC
COURSE NAME: PHYSICALCHEMISTRY
SESSION: JUNE 2023
DURATION: 3 HOURS
LEVEL: 6
COURSE CODE: PCH602S
PAPER: THEORY
MARKS: 100
EXAMINER{S)
FIRST OPPORTUNITY EXAMINATION QUESTION PAPER
Prof Habauka M Kwaambwa
MODERATOR: Dr Euodia Hess
INSTRUCTIONS
1. Answer ALL the questions in Sections A and B.
2. Write clearly and neatly.
3. Number the answers clearly.
PERMISSIBLE MATERIALS
Non-programmable Calculators
ATTACHMENT
List of Useful Constants and Equation
THIS QUESTION PAPER CONSISTS OF 9 PAGES (Including this front page and a list of useful
constants and equation as an attachment)
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SECTIONA: MULTIPLE CHOICEQUESTIONS
[20]
There are 20 questions in this section. Answer ALL questions by selecting the letter of the
correct answer. Each question carries 2 marks.
1. The heating of a gas at constant pressure is governed by
A. Boyle's law
B. Charles' law
C. Gay Lussac law
D. Avogadro's law
E. Ideal gas equation of state
2. An ideal gas is expanded to twice its original volume during an isothermal process. The
final pressure of the gas
A. Increases to less than twice its original value
B. Decreases to twice its original value
C. Increases to more than twice its original value
D. Does not change
E. Decreases to one-half its original value
3. A sample of an ideal gas in a rigid closed container at a temperature of 50°C and 1.5
atm is heated to 100°C. What is the pressure of the gas at the higher temperature?
A. 3 atm
B. 3.5 atm
C. 1.7 atm
D. 4.6 atm
E. Insufficient information
4. What is the volume of 2 moles of a gas at STP?
A. 22.4 dm 3
B. 48.8 dm 3
C. 67.2 dm 3
D. 44.8 dm 3
E. Insufficient information
5. A closed system is one in which
A. Heat does not cross boundary of the system but mass may do so.
B. Both mass and energy cross the boundary of the system
C. Neither mass nor energy crosses the boundary of the system
D. Mass crosses the boundary but not the energy
E. Thermodynamic reactions do not occur
6. An intensive property of a system is one whose value
A. depends on the mass of the system like volume.
B. is not dependent on the path taken followed but on the state.
C. is dependent on the path followed and not on the state.
D. is always constant.
E. does not depend on the mass of the system, like temperature, pressure, etc.
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7. If a gas is compressed against a constant pressure, keeping the temperature constant,
then work done will be equal to:
A. Positive
B. Negative
C. Zero
D. Pressure x Volume
E. May be positive or negative depending on the temperature used
8. A mixture of gas expands from 0.06 m3 to 0.09 m3 at a constant pressure of 1 x 106 Pa
and the change in internal energy is 54 kJ during the process. The heat absorbed by
the mixture is
·
A. 30 kJ
B. 54 kJ
C. 84 kJ
D. 100 kJ
E. Insufficient information
9. The heat absorbed or given out by a reaction at constant pressure is known as:
A. Entropy change
B. Work
C. Enthalpy change
D. Internal energy change
E. None of the above
10. In a certain process, 900 J of work is done by the system which absorbs 550 J of heat.
What is change in internal energy (LiU) for the process?
A. 900 J
B. 250 J
C. 1450 J
D. -1459 J
E. - 350 J
11. For iodine, '2, at 114°C, the standard enthalpy of fusion, Li Htusion, is 16.1 kJmoI-1 and
the standard enthalpy of vaporization, Li Hvap, is 45.0 kJmoI-1. Calculate the standard
enthalpy of sublimation at this temperature.
A. 61.1 kJmoI-1
B. 16.1 kJmoI-1
C. 25.0 kJmoI-1
D. 28.9 kJmoI-1
E. Insufficient information
o- 12. The conductivity for an acid HA solution of 0.0316 M concentration is 9.260 1m-1.
o- Calculate the molar conductivity (in 1m2mol- 1) of the solution.
A. 2.93
B. 2.93 X 102
C. 0.293
D. 2.93 x 10-2
E. None of the above
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13. The degree of dissociation of an acid HX in aqueous solution of concentration 0.025
moldm- 3 is 0.028. What is the Kafor the acid?
A. 7.2 X 10-4
B. 2.0 X 10-S
C. 8.1 X 10-4
D. 1.8 X 10-5
E. 2.0 X 10-4
14. The molar conductivities of cs+ and SO~- are 0.772 x 10-2 and 1.600 x 10-2 Sm2mo1-1,
respectively. What is the molar conductivity
A. 3.972 x 10-2 Sm2mo1-1
B. 3.144 x 10-2 Sm2mol- 1
C. 0.828 x 10-2 Sm2mo1-1
D. 2.372 x 10-2 Sm2mo1-1
of Cs2SO4?
E. Insufficient information
15. The molar conductivity of Mg{NO3)z is 2.488 x 10-2 Sm2mo1-1. If the molar conductivity
of Mg 2+ is 1.060 x 10-2 Sm2mo1-1, what is the molar conductivity of NO~?
A. 0.368 x 10-2 Sm2mo1-1
B. 1.428 x 10-2 Sm2mo1-1
C. 0. 714 x 10-2 Sm2mo1-1
D. 0.184 x 10-2 Sm2mo1-1
E. Insufficient information
16. The molar conductivities at infinite dilution, Ao, for HCl{aq), NaB{aq)
benzoate) and NaCl (aq) are 426.2, 82.4 and 126.5 Scm2mo1-1, respectively,
What is Aofor HB {benzoic acid) in Sm2mo1-1?
{sodium
at 25°C.
A. 0.382
B. 3.82 X 102
C. 3.82
D. 3.82 x 10-2
E. None of the above
17. What are the units of k tor the rate law, Rate = k [~], , when the concentration and
time units are mol/L and seconds, respectively?
A. s-1
B. L mo1-1 s-1
C. L2 mo1-2 s-1
D. L2 s2 mo1-2
E. L-2s-2mo1-2
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18. A reaction A P displays first-order kinetics. It therefore follows that a plot of
____
versus time is linear, and that the slope of this plot= ___ _
A. [A]; -k
B. [A]; k
C. 1/[A]; -k
D. 1/[A]; k
E. ln[A); -k
19. The activation energy of a reaction can be determined from the slope of which of the
following graphs?
A. Ink vs T
B. -Ivnsk -I
TT
C. Ink vs -I
T
D. -vTs-
I
Ink T
E. -Ivnsk-
I
T
T
20. The ozone, 03, of the stratosphere can be decomposed by the reaction with nitrogen
oxide {commonly called nitric oxide), NO, from high-flying jet aircraft.
O3{g)+ NO{g) NOz{g)+ Oz{g)
The rate expression is rate= k[O3)[NO]. Which of the following mechanisms agree
with observed rate expression?
Mechanism 1
NO+ 03 NO3+ 0
slow
fast
Mechanism 2
one slow step
Mechanism 3
slow
fast
Mechanism 4
N+O
03 + 0 202
Oz+ N NO2
A. 1 only
B. 1 and 2
C. 2, 3 and 4
D. 2 only
E. All the 4 mechanisms
slow
fast
fast
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SECTION B
[60]
There are FOUR questions in this section. Answer all Questions.
QUESTION 1
[12]
(a) State whether q, w, llU, llH and llS are positive, negative or zero for reversible
adiabatic compression of an ideal gas.
(5)
(b) Predict whether the entropy change,~, is greater than zero, less than zero or zero
for each of the following processes:
(7)
(i)
Dissolving a solute in a solvent to produce a solution
(ii) An ideal gas undergoing a Carnot cycle
(iii) Cl(g) Cl"(g)
(iv) Water frozen at 0°C and 1 atm
(v) CH3CH2CH(3g) + 5O2(g) 3CO2(g)+ 4H2O(/)
(vi) H2(g, 300 K, 1 atm) H2(g, 100 K, 1 atm)
(vii) Cl2(g)+ H2(g) 2HCl(g)
QUESTION 2
[12]
Using the First Law of Thermodynamics, calculate the quantity listed in bold, in joules, for the
system of one mole of gas in a cylinder with movable cylinder piston.
[Given: Cv= 12.5 JK-1mo1-1; Cp= 20.8 JK-1mo1-1J
(a) The gas absorbs 234 J of heat and is compressed by 534 J of work. ~U = ?
(b) The gas is cooled by removing 106 J of heat and expands doing 242 J of work. ~U =?
(c) The gas is heated at constant pressure from 298 K to 398 K. q =?
(d) The gas is heated at constant volume from 298 K to 398 K? ~U =?
(e) The gas expands from 0.250 L to 1.00 L against an external pressure of 2.50 atm. w = ?
(f) The change internal energy (~U) for a constant pressure process was - 407 J and the
change in enthalpy was - 687 J. w =?
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QUESTION 3
[14]
(a) Define the terms conductance, L, and resistivity, p, as used in Electrochemistry and
state the SI units.
(4)
(b) A conductivity cell was calibrated using 0.01M KCI(K=l.4087 x 10-3 Scm·1) in the cell,
and the measured resistance was 688 0.
(i)
Find the cell constant.
(3)
(ii) A 0.010 M AgNO3 solution in the same cell had a resistance of 777 n. What is
the conductivity, K, for the AgNO3solution?
(3)
(c) Given the standard reduction potentials - 0.403 V and 0.337 Vat 298 K for the half
cells Cd2+lcd(s) and Cu2+ICu(s), respectively. Deduce the overall reaction that will be
spontaneous and write down the complete cell notation for this overall reaction. (4)
QUESTION 4
[22]
(a) What is the overall order of the reaction described by each of the rate expressions
below? State the units of the rate coefficient, k, if the rate is in moldm· 3s·1.
(i) Rate= k[AJ2 [B]
(ii) Rate =k[A)15 [B]5°
(4)
(b) Consider a reaction A
[A]-[AL =-kt
P. The integrated rate law for the reaction is:
(i) State the two reaction requirements needed in order to derive the equation
above.
(2)
(ii) What is the order of the reaction? What are the units of the rate constant if
the rate is in mol L·1 min•1?
(2)
(iii) What plot would you construct to determine the rate constant, k, for the
reaction? Label the axes on diagram and sketch the graph that you would
expect.
(3)
(iv) Derive the half-life expression for this reaction.
(3)
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(c) The table below gives experimental data for the half-lives, t0_5 , of different reactions
as a function of the initial reactant concentration, Co. Determine the order of each of
the two reactions.
(4)
to.sI seconds
Co/ moldm- 3
Reaction 1 Reaction 2
0.02
30
60
0.04
30
120
(d) The following questions refer to the popular demonstration called "Elephants
Toothpaste" in which the mechanism is believed to be:
Step 1:
H202 + 1- H20 + QI-
slow
Step 2:
H202 + QI- H20 + 02 + 1-
fast
(i)
Identify the catalyst.
(1)
(ii) Identify the intermediate.
(1)
(iii) Devise the overall chemical equation consistent with the mechanism provided.
(1)
(iv) Devise the rate law.
(1)
ENDOF EXAMQUESTIONS
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LIST OF USEFUL EQUATION AND CONSTANTS
Van der Waals eq!l.
P= nRT
V-nb
v2 n-,a
---
=----RT
V-b
a
2
V
Universal Gas constant
Boltzmann's constant,
Planck's constant
Debye-Huckel's constant,
Faraday's constant
Mass of electron
Velocity of light
Avogadro's constant
1 electron volt (eV)
R=
k=
h=
A=
F=
me =
C
=
NA =
=
8.314 J K-1 mo1-1
1.381 x 10-23 J K-1
6.626 X 10-34 J S
0.509 {mol dm-3)112 or mo1-0·5kg05
96485 C mo1-1
9.109 X 10-31 kg
2.998 x 108 m s-1
6.022 X 1023
1.602 X 10-19 J
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