PHYSICAL CHEMISTRY IN BRIEF

CHAP. 7: PHASE EQUILIBRIA [CONTENTS] 208

7.7.4 Effect of temperature and pressure on gas solubility

Effect of temperature
Temperature affects gas solubility through of Henry’s constant in (7.40). Conversion ofKH
from one temperature to another is performed using the formula

lnKH(T 2 ) = lnKH(T 1 )−

∫T 2

T 1

H

⊗

2

RT^2

dT , (7.47)

whereH
⊗
2 =H^2 −H

⊗
m, 2 is the differential heat of solution of the gaseous component in a given
solvent [see equation (6.56)].

7.7.4.1 Effect of pressure.

Pressure affects gas solubility both directly and through of Henry’s constant.

• The direct effect is evident from relation (7.42), according to which solubility increases
  linearly with a growing partial pressure.


• The effect of pressure on Henry’s constant is given by the relation

KH(p 2 ) =KH(p 1 ) +

∫p 2

p 1

V

∞

2

RT

dp , (7.48)

whereV

∞

2 is the partial molar volume of gas dissolved in the liquid phase at infinite

dilution. Given the small value ofV

∞

2 /(RT), this effect is rather weak.

7.7.5 Other ways to express gas solubility.

Gas solubility may be also expressed by the volume of gas dissolved in a unit volume of the
solvent. Based on the way in which the volume of the dissolved gas is defined, we distinguish
two different cases (in both of them we assume the validity of the equation of state of an ideal
gas).

• Bunsen’s absorption coefficient—the volume of the dissolved gas is calculated at the
  standard temperatureTst= 273.15 K and a given partial pressurep 2. Then

α=

VT(g)st

V

(`)

1

. (7.49)