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Chemical Oceanography, 4th Edition
have similar thermodynamic properties, and the interaction is frequently called hydrophobic bonding.
The addition of an electrolyte to water interferes with the gas dissolution and the organization of water around the gas. This frequently results in a decrease in the solubility, or
a “salting out.” This salting out is frequently a linear function of the molar ionic strength:
log C = log C° + k I V
(6.53)
When k is negative, the result is a salting out, and when k is positive, the result is a salting
in. Values of k for various gases in seawater are given in Table 6.9. The ratio of the solubility
in water to the value in seawater is equal to the activity coefficient of the gas:
γ g = C°/C
(6.54)
Values of γ g for various gases are also given in Table 6.10.
Table 6.8
Values of ΔH and ΔS for the Solution
of Gases in Water (25°C)
Gas
ΔH (kcal mol –1 )
ΔS (cal deg mol –1 )
H 2
1.3
26
N 2
2.1
29
He
0.8
27
Ne
1.9
29
Ar
2.7
30
Kr
3.6
32
Xe
4.5
34
Rn
5.1
34
CO
3.9
30
O 2
3.0
31
NO
2.7
29
CO 2
4.7
31
COS
5.8
35
N 2 O
4.8
32
CH 4
3.2
32
Table 6.9
Comparison of the Measured and Calculated Salting
Coefficients of Gases in Seawater and NaCl at t = 25°C
Gas
Seawater
NaCl
Measured
Calculated
Measured
Calculated
He
0.092
0.099
0.090
0.100
Ne
0.102
0.099
0.106
0.100
Ar
0.122
0.123
0.131
0.122
O 2
0.122
0.135
0.142
0.134
N 2
0.132
0.144
0.141
0.143