Environmental Engineering Reference
In-Depth Information
The respective equilibrium constants for the reactions can be written in terms of
Henry's constants for SO
2
as follows:
HSO
3
l
H
+
l
[SO
2
·
=
HSO
3
l
H
+
l
·
K
aw
P
SO
2
K
s
1
=
(4.19)
H
2
O]
l
SO
2
3
l
H
+
2
K
aw
K
s
1
P
SO
2
K
s
2
=
·
.
(4.20)
l
The total concentration of SO
2
that exists in the various forms [SO
2
.H
2
O]
l
, [HSO
3
]
l
,
and [SO
2
−
3
]
l
is given by
1
.
P
SO
2
K
s1
H
+
l
+
K
s1
K
s2
H
+
2
l
[SO
2
]
T
=
K
aw
·
+
(4.21)
The apparent air-water partition constant,
K
aw
, defined by
P
SO
2
[
SO
2
]
T
is given by
K
aw
K
aw
=
1
K
s1
K
s2
H
+
2
l
.
(4.22)
+
K
s1
H
+
l
+
Thus as [H
+
]
l
increases (or pH decreases), more and more of SO
2
appears in solution
in the form of bisulfite and sulfite ions. Therefore the apparent partition constant
decreases. For the SO
2
dissolution,
K
s1
=
10
−
8
M
0.0129 M and
K
s2
=
6.014
×
(Seinfeld, 1986).
The dissolution of CO
2
in water is similar to that of SO
2
in that three different
reaction equilibria are possible. These and the respective equilibrium constants are
given below:
P
CO
2
[CO
2
·
H
2
O
(
l
)
;
K
aw
=
CO
2
(
g
)
+
H
2
O
(
l
)
CO
2
·
,
(4.23)
H
2
O]
l
HCO
3
l
H
+
l
[CO
2
·
H
+
(
l
)
HCO
3
(
l
)
;
K
c1
=
CO
2
·
H
2
O
(
l
)
+
,
(4.24)
H
2
O]
l
CO
2
3
l
H
+
l
HCO
3
(
l
)
H
+
(
l
)
CO
2
−
3
+
(
l
)
;
K
c2
=
HCO
3
l
.
(4.25)
The apparent air-water partition constant is given by
K
aw
K
aw
=
1
K
c1
K
c2
H
+
2
l
.
(4.26)
+
K
c1
H
+
l
+
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