Chemical Kinetics Question Paper

Chemical Kinetics

Course:Bachelor Of Science

Institution: Kenyatta University question papers

Exam Year:2009

KENYATTA UNIVERSITY
UNIVERSITY EXAMINATIONS 2009/2010
FIRST SEMESTER EXAMINATION FOR THE DEGREE OF BACHELOR OF
SCIENCE AND BACHELOR OF EDUCATION (SCIENCE)

SCH 305:
CHEMICAL KINETICS

DATE: Tuesday, 29th December, 2009

TIME: 11.00 a.m. – 1.00 p.m.
------------------------------------------------------------------------------------------------------------
INSTRUCTIONS:
Answer ALL FOUR questions.
Useful data:
R = 8.314 J mole –1 K-1
0oC = 273.15K

Q.1. a)
Write concisely to distinguish between molecularity and order of a
chemical
reaction.
(4
marks)

b)
Derive the kinetic equation for a second order reaction, in a single
substance, and show the half-life as a function of the initial reactant
concentration.
(6
marks)

c)
In the decomposition of gaseous ethanal at 518oC, the time taken to
decompose half the material was found to be 410 sec, when the initial
pressure was 363 mmHg and 880 sec for the initial pressure of 169
mmHg. Work out the apparent order of the reaction.
(5 marks)

d)
Account for the effect of temperature on the rate of a chemical reaction.

(4 marks)
Page 1 of 3

Q.2
a)
Explain, using a suitable example, the essential features of a chain
reaction.

(6 marks)

b)
The decomposition of nitrogen (IV) oxide, according to the equation:
2NO2(g) ? 2NO(g)+O2(g) ,
obeys second order kinetics. The following table gives the specific
reaction rate constant, k, at four temperatures:
T,
K
592
603.2
627
651.5
k(mol-1ls-1)
0.522
0.755
1.70
4.020
Determine, graphically, the value of the activation energy of the reaction.

(8 marks)

c)
With the aid of the stationary-state concept, derive the rate law for the
following mechanism:

k1
A

B (fast)

k2

k3
B

C

(slow)

(4 marks)

Q.3
a)
The hydrolysis of methyl acetate (in the presence of dilute hydrochloric
acid as a catalyst) shows first order kinetics and is represented thus:
CH3COOCH3 + H2O
??
? +
H
CH3COOOld + CH3OH.
The reaction is followed by titrating constant volumes of the reaction
mixture with standard sodium hydroxide. The following data were
obtained:

Page 2 of 3

t, sec

Titre, cm3
0
24.36
1200
25.85

4500
29.32
7140
31.72
8
47.15
Determine the value of the specific rate constant through a graphical
method. (10
marks)

b)
The rate equation for a reaction of nth order in substance A is represented
thus:
d
-
[ ]
A = K [ ]n
A
dt
Show that the half-life is given by:
n
? 2 1- - 1?
Ln t = Ln
- -
A
1
(n )1Ln
?
?
?
?
o, where Ao is the initial molar concentration
2
k(n -1
?
?
of
substances
A.
(7
marks)

Q.4
a)
Write concisely on the kinetics of heterogeneous unimolecular gas
reactions at low and high pressures.

(8 marks)

b)
Give the Arrhenius kinetic equation and explain two ways in which this
equation may be used to determine the activation energy of a chemical
reaction.

(8 marks)

Page 3 of 3

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