Environmental Engineering Reference
In-Depth Information
5.26 3 Sedlak and Andren (1994) showed that the aqueous-phase oxidation of
polychlorinated biphenyls (PCBs) by OH X is influenced by the presence
of
A P k 1
k 1 A + P,
k 2
−−→ A OH
A + OH
particles such as diatomaceous earth (represented as P). The mecha-
nism representing this is given below, where A-OH is the hydroxylated
PCB. Using appropriate assumptions derive the following equation for the
concentration of A in the aqueous phase:
[ A ]
[ A ] 0 =
k 1
( β − α ) ( e −α t
e −β t ) ,
where αβ = k 1 k 2 [ OH ] and α + β = k 1 + k 1 [ P ]+ k 2 [ OH ] .For
2,2 ,4,5,5 -pentachlorobiphenyl, k 1 = 4.53 × 10 4 s 1 , k 2 = 1.41 L/g s,
and k 2 =
10 9 cm 3 /mol s.At an average concentration of [OH X
]=
1 × 10 14 mol/L, and [ P ] / [ Fe ]= 10 μ M, sketch the progress of hydroxy-
lationofPCB.Repeatyourcalculationfor [ P ]= 50 μ M.Whatconclusions
can your draw from your plots?
5.27 2 The photochemical reaction in the upper atmosphere that leads to the
formation and dissipation of O 2 follows the following pathway:
4.6
×
h
ν
−−→ O ( 1 D ) + O,
O 2
k 2
−−→ O + M.
O ( 1 D ) + M
O( 1 D) is a transient state (singlet) for O atom and M is a third body
such as N 2 . The rate of the first reaction is represented as R 1 .If [ M ]=
10 14 molecules/cm 3 and k 2 = 1 × 10 25 cm 6 /(molecule) 2 s, determine
the steady-state concentration of singlet oxygen as a function of R 1 .
5.28 2 Atmospheric photo-oxidation of propane to acetone is said to occur by the
following pathway:
CH 3 CH 2 CH 3 + OH −→ CH 3 CH CH 3 + H 2 O,
fast
CH 3 CH CH 3 + O 2
−−→ CH 3 CH 2 ( O 2 ) CH 3 ,
CH 3 CH 2 ( O 2 ) CH 3 + NO −→ NO 2 + CH 3 CH ( O ) CH 3 ,
CH 3 CH ( O ) CH 3 + O 2
fast
−−→ CH 3 COCH 3 + HO 2 .
Obtain an expression for the rate of production of NO 2 due to the
dissipation of propane. Make appropriate assumptions.
5.29 3 Atmospheric chemists consider the oxidation of CH 4 by OH to be a
convenient way of estimating the concentration of hydroxyl ion in the
atmosphere: CH 4 + OH
k
CH 3 + H 2 O. In so doing, it is assumed that
the hydroxyl radical concentration is constant, since it is much larger than
the methane concentration. Given that k = 107 m 3 /mol s at 300 K and that
 
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