Henry’s law

Henry’s law

source : scied.ucar.edu

Henry’s Law —

This law gives a relationship between  solubility of a gas  &  its pressure . According to this law,

“The mass of a gas dissolved per unit volume of  the solvent at a given temperature is proportional to the pressure of the gas in equilibrium with the solution.”

m =mass of gas, p =pressure of gas,K = proportionality constant
m = K p

Factors affecting ‘K’ –

a) Nature of gas

b) Nature of solvent

c) Temperature

d)Unit of pressure

When solubility of gas is plotted against pressure at a given temperature, a straight line passes through origin is obtained.

Straight line graph shows the validity of Henry’s law.

When a number of gases are present in the solvent then according to Henry’s law,

x₂    p₂

x₂ =K’ p₂

p₂ =K x₂      ( K =1/K’ )

x₂ = mole fraction of gas

p₂= partial pressure of gas

K =Henry’s law constant

Alternatively Henry’s law is,

The pressure of a gas over a solution in which the gas is dissolved is directly proportional to the mole fraction of the gas.

Limitations –

1. Pressure is not high .
2. Temperature is not too low.
3. The gas is not highly soluble .
4. The gas neither reacts chemically with solvent nor dissociate or associate in the solvent.