Environmental Engineering Reference
In-Depth Information
Whatcanyouinferregardingthemechanismofdecompositionofozone
in solution?
5.12
2
The oxidation of polyaromatic hydrocarbons is an important reac-
tion in atmospheric chemistry. The reaction between benzene and
oxygen was studied by Atkinson and Pitts (1975) at various
temperatures.
T
(K)
k
(L/mol/s)
1.44
×
10
−
7
300
3.03
×
10
−
7
341
6.9
×
10
−
7
392
Obtain,
E
a
, for the above reaction.
5.13
2
The atmospheric reaction between methane (CH
4
)
and hydroxyl radical
(OH
!
)
is of importance in understanding the fate of several hydrocarbon
pollutants in the air environment. An activation energy of 15 kJ/mol and a
rate constant of 3
×
10
−
12
cm
3
/molecule/s were determined in laboratory
experiments for the reaction. Using the temperature profiles in the atmo-
sphere (Chapter 2), determine the rate constants for this reaction at various
altitudes. The approximate distances of the various layers from ground
level are (i) atmospheric boundary layer (
=
0.1 km), (ii) lower troposphere
(
=
1 km), (iii) middle troposphere (
=
6 km), and (iv) lower stratosphere
(
=
20 km).
5.14
3
The thermal decomposition of alkane (e.g., ethane) is of importance in
environmental engineering (e.g., combustion kinetics of petroleum hydro-
carbons). A chain reaction mechanism is proposed. Identify the initiation,
propagation, and termination steps in the reaction. Using the steady-state
approximation obtain the overall rate of decomposition of ethane.
k
1
−−→
2CH
3
,
CH
3
+
C
2
H
6
C
2
H
6
k
2
−−→
C
2
H
5
+
CH
4
,
k
3
−−→
C
2
H
5
H
•
,
C
2
H
4
+
k
4
H
•
+
C
2
H
6
−−→
C
2
H
5
+
H
2
,
k
5
−−→
n
−
C
4
H
10
,
2C
2
H
5
k
6
−−→
C
2
H
4
+
C
2
H
6
.
2C
2
H
5
5.15
3
The concentrations of some major ions in natural waters are given below.
Concentration (mmol/kg)
Na
+
K
+
Ca
2+
Mg
2+
Cl
−
SO
2
4
NO
3
F
−
Medium
Seawater
468
10
10.3
53
546
28
0.05
0.07
Riverwater
0.27
0.06
0.37
0.17
0.22
0.12 0.02
0.005
Fogwater
0.08 —
0.2
0.08
0.2
0.3
—
1
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