Encyclopedia of Environmental Science and Engineering, Volume I and II

WATER CHEMISTRY 1271

TABLE 4

Equilibrium constants of redox processes pertinent in aquatic conditions (25C)

Reaction pε°( log K) pε°(W)a

(1) 1/4 O 2 (g)  H (W)  e  1/2 H 2 O 20.75 13.75

(2) 1/5 NO 3   6/5H (W)  e  1/10 N 2 (g)  3/5 H 2 O 21.05 12.65

(3) 1/2 MnO 2 (S)  1/2HCO 3   3/2 H (W)  e

 1/2MnCO 3 (s)  3/8 H 2 O

20.46 9.96

8.46

(3a) 1/2 MnO 2 (s)  2H (W)  e  1/2 Mn^2   H 2 O 20.42 6.42

(4) 1/2 NO 3   H (W)  e  1/2 NO 2  1/2 H 2 O 14.15 7.15

(5) 1/8 NO 2  5/4 H (W)  e  1/8 NH 4  3/8 H 2 O 14.90 6.15

(6) 1/6 NO 2   4/3 H^ (W)  e  1/6 NH 4   1/3 H 2 O 15.14 5.82

(7) 1/2 CH 3 OH  H (W)  e  1/2 CH 4 (g) 

1/2 H 2 O

9.88 2.88

(8) 1/4 CH 2 O  H (W)  e  1/4 CH 4 (g)  1/4 H 2 O 6.94 0.06

(9) FeOOH(s) HCO 3  2H (W)  e  FeCO 3 (s) 

2H 2 O

15.33 1.33

1.67b

(9a) Fe^3   e  Fe^2  12.53  12.53

(10) 1/2 CH 2 O  H (W)  3  1/2 CH 3 OH 3.99 3.01

(11) 1/6 SO 42   4/3 H (W)  e  1/6 S(s)  2/3 H 2 O 6.03 3.30

(12) 1/8 SO 42   5/4H (W)  3  1/8 H 2 S(g) 

1/2 H 2 O

5.75 3.50

(13) 1/8 SO 42   9/8 H (W)  e  1/8 HS  1/2 H 2 O 4.13 3.75

(14) 1/2 S(s)  H (W)  e  1/2 H 2 S(g) 2.89 4.11

(15) 1/8 CO 2 (g)  H (W)  e  1/8 CH 4 (g)  1/4 H 2 O 2.87 4.13

(16) 1/6 N 2 (g)  4/3 H (W)  e  1/3 NH 4  4.68 4.68

(17) 1/2 (NADP) 1/2 H (W)  e 1/2 (NADPH) 2.0 5.5c

(18) H (W)  e  1/2 H 2 (g) 0.0 7.00

(19) Oxidized ferredoxin  e  reduced ferredoxin 7.1 7.1d

(20) 1/4 CO 2 (g)  H (W)  e  1/24 (glucose) 

1/4 H 2 O

0.20 7.20e

(21) 1/2 HCOO  3/2H (W)  e  1/2 CH 2 O 

1/2 H 2 O

2.82 7.68

(22) 1/4 CO 2 (g)  H (W)  e  1/4 CH 2 O  1/4 HO 2 1.20 8.20

(22a) 1/4 HCO 3  5/4 H (W)  e  1/4 CH 2 O 

1/2 H 2 O

0.76 7.99

8.74b

(23) 1/2 CO 2 (g)  1/2 H (W)  e  1/2 HCOO 4.83 8.73

(24) 1/2 C1 2 (aq)  e  C1 23.6 23.6

(25) HOCl  H (W)  e  1/2 C1 2 (aq)  H 2 O 26.9 19.9

a (W) signifies that the pH  7.

b These data correspond to (HCO

3

)  10  (^3) M rather than unity and so are not exactly pε(W); they represent
typical aquatic data conditions more nearly than pε(W) values do.
c M. Calvin and J.A. Bassham, The Photosynthesis of Carbon Compounds, Benjamin, New York, 1962.
d D. I. Arnon, Science, 149, 1460 (1965).
e A. L. Lehninger, Bioenergetics, Benjamin, New York, 1965:
Table from Stumm, W. and J. Morgan, Aquatic Chemistry, Wiley-Interscience, New York, 1970, p. 318.
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