CHAP. 7: PHASE EQUILIBRIA [CONTENTS] 209
In relation (7.49),VT(g)st=n 2 RTst/p 2. More often we may encounter the form
α=
Vstpst
V
(`)
1 p^2
=
n 2 RTst
n 1 V
(`)
m, 1 p^2
, (7.50)
whereVst=n 2 RTst/pstis the volume of the dissolved gas calculated from the equation
of state of an ideal gas atTst= 273.15 K andpst= 101.325 kPa. V 1 (`)=n 1 Vm(`,) 1 is the
volume ofn 1 moles of the solvent at a given temperature and pressure.
- Ostwald’s absorption coefficient—the volume of the dissolved gas is calculated at a
given temperature and a given partial pressure.
β=
V 2 (g)
V 1 (`)
, (7.51)
whereV 2 (g)=n 2 RT /p 2 is the volume of the dissolved gas calculated from the equation
of state of an ideal gas at the temperature of the system and a partial pressurep 2.
U Main unit:dimensionless quantity.
- Conversions between coefficients
α=β
Tst
T
. (7.52)
The molar fraction of gas in the liquid phase,x 2 , may be calculated from the absorption
coefficients using the equation
x 2 =
1 + RT
Vm(`,) 1 p 2 β
− 1
=
1 + RT
st
Vm(`,) 1 p 2 α
− 1
(7.53)
Example
1 dm^3 of gaseous CO 2 dissolves in 1 dm^3 of water at 17◦C and a partial pressure of carbon
dioxidepCO 2 = 101. 32 kPa. Calculate Bunsen’s and Ostwald’s absorption coefficients.
