What is Henry's Law of Solubility ?

Henry's Law:

(1) The solubility of a gas in a liquid is determined by several factors. In addition to the nature of the gas and the liquid, solubility of the gas depends on the temperature and pressure of the system.

(2) The solubility of a gas in a liquid is governed by Henry's law which states that the solubility of a gas in a liquid is directly proportional to the pressure of the gas.

(3) Dalton, a contemporary of Henry, also concluded independently that the solubility of a gas in a liquid solution is a function of the partial pressure of the gas. If we use the mole fraction of the gas in the solution as a measure of its solubility, then: Mole fraction of the gas in a solution is proportional to the partial pressure of the gas.

Or, partial pressure of the gas in solution = K_H ´ mole fraction of the gas in solution

Here K_H is Henry's law constant

                                  p = K_H X _(Solute)

If we draw a graph between partial pressure of the gas versus mole fraction of the gas in solution, then we should get a plot of the straight line passing through origin.

Experimental result for the solubility of HCl gas in Cyclohexane at 93 K the slope of line is the Henry's law constant

Different gases have different K_H values at the same temperature. This suggests that K_H is a function of the nature of the gas. Table gives K_H values of some common gases at specified temperature

Values of Henry's law constant (K_H) for some selected gases in water:

It is obvious from figure that the higher the value of K_Hat a given pressure, the lower is the solubility of the gas in the liquid. It can be seen from table that K_H value for both N₂ and O₂ increases with increase in temperature indicating that solubility of gases decreases with increase of temperature. It is due to this reason that aquatic species are more comfortable in cold waters rather than warm waters.