Agriculture Reference
In-Depth Information
Table 4.1
Equilibrium constants of important reduction half-reactions in
natural systems at 25
◦
C
pe
o
=
log
K
H
H
+
+
1
2
H
2
(
g
)
e
−
=
0.00
4
O
2
(
aq
)
+
H
+
+
e
−
1
2
H
2
O
=
20.75
6
N
2
+
4
3
H
+
+
e
−
1
3
NH
4
+
=
4.63
1
2
NO
3
−
+
H
+
+
e
−
1
2
NO
2
−
+
1
2
H
2
O
=
14.15
1
6
NO
2
−
+
4
3
H
+
+
e
−
1
6
NH
4
+
+
1
3
H
2
O
=
15.14
1
4
NO
3
−
+
5
4
H
+
+
1
8
N
2
O(g)
5
8
H
2
O
e
−
=
+
18.81
1
5
NO
3
−
+
6
5
H
+
+
1
10
N
2
(
g
)
+
3
5
H
2
O
e
−
=
21.05
2
SO
4
2
−
+
H
+
+
e
−
2
SO
3
2
−
+
1
1
2
H
2
O
=
−
1.65
8
SO
4
2
−
+
8
HS
−
+
1
9
8
H
+
+
e
−
1
1
2
H
2
O
=
4.25
1
4
SO
4
2
−
+
5
4
H
+
+
e
−
1
8
S
2
O
3
2
−
+
5
8
H
2
O
=
4.85
1
8
SO
4
2
−
+
5
4
H
+
+
e
−
1
8
H
2
S(g)
+
1
2
H
2
O
=
5.25
Mn
1
2
MnO
2
(
s
)
+
2H
+
+
e
−
1
2
Mn
2
+
+
2H
2
O
=
21.82
MnOOH(s)
+
3H
+
+
e
−
=
Mn
2
+
+
2H
2
O
25.33
1
2
Mn
3
O
4
(
s
)
+
4H
+
+
e
−
3
2
Mn
2
+
+
2H
2
O
=
30.79
Fe
Fe
3
+
+
e
−
=
Fe
2
+
13.00
3H
+
+
Fe
2
+
+
α
-FeOOH(s)
+
e
−
=
2H
2
O
11.31
Fe(OH)
3
(
s
)
+
3H
+
+
e
−
=
Fe
2
+
+
3H
2
O
16.54
C
1
2
CH
2
O
+
H
+
+
e
−
1
2
CH
3
OH(aq)
=
3.99
1
4
CH
2
O
+
H
+
+
e
−
1
4
CH
4
(
g
)
+
1
4
H
2
O
=
6.94
1
2
CO
2
(
g
)
+
1
2
H
+
+
e
−
1
2
HCOO
−
=
−
5.22
1
4
CO
2
(
g
)
+
H
+
+
e
−
1
4
HCHO(aq)
+
1
2
H
2
O
=
−
1.20
1
6
CO
2
+
H
+
+
e
−
1
6
CH
3
OH(aq)
+
1
6
H
2
O
=
0.50
1
8
CO
2
(
g
)
+
H
+
+
e
−
1
8
CH
4
(
g
)
+
1
4
H
2
O
=
2.87
1
4
CO
2
(
g
)
+
7
8
H
+
+
1
8
CH
3
COO
−
+
1
4
H
2
O
e
−
=
1.27
1
5
CO
2
(
g
)
+
H
+
+
1
10
CH
3
CHO
(
g
)
+
3
10
H
2
O
e
−
=
0.99
1
6
CO
2
(
g
)
+
H
+
+
e
−
1
12
CH
3
CH
2
OH(aq)
+
1
4
H
2
O
=
1.52
1
6
CO
2
(
g
)
+
H
+
+
e
−
1
12
C
2
H
4
(
g
)
+
1
4
H
2
O
=
1.34
1
4
CO
2
(
g
)
+
11
12
H
+
+
e
−
1
12
(
lactate
)
+
1
4
H
2
O
=
0.68
3
10
CO
2
(
g
)
+
10
H
+
+
e
−
9
1
10
(
pyruvate
)
+
3
10
H
2
O
=
0.05
1
4
CO
2
(
g
)
+
H
+
+
e
−
1
24
(
glucose
)
+
1
4
H
2
O
=
−
0.20
Source
: Morel and Herring (1993) and Stumm and Morgan (1996).
