Gases in Solution
Methods of expressing gas solubility
1. Bunsen coefficient, α
Volume of gas reduced to 0 °C and 760mmHg absorbed by unit volume of solvent
2. Ostwald coefficient, L
Ratio of the volume of gas absorbed to the volyme of the absorbing liquid at the same temperature
3. Henry's Law constant, KH
Allows prediction of the equilibrium constant of the dissolved gas regardless of any following or coupled reactions
Dalton's Law
The partial pressure of a gas A, PA in a mixture is the pressure that the gas would exert if it alone filled the container.
For an ideal gas
Consider the partial pressure PA
where KH - Henry's constant
Note:
i) Partial pressure = mol fraction x total pressure
ii) In calculating the concentration of dissolved gas, account needs to be taken of the vapour pressure of water
Clausius - Clapeyron equation
In the absence of chemical reactions, ΔS is negative and therefore -TΔS is postive
Gases spontaneously dissolve and therefore ΔH is negative
For low concentration:
where c1 and c2 are the two concentrations at temperature T1 and T2
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