Introductory University Chemistry I. Henry's Law and the Solubility of Gases Introductory University Chemistry I Solutions and Solubility Henry's Law and the Solubility of Gases Concentration of solutions was taken up as part of molar stoichiometry in earlier sections of introductory university chemistry. The concentrations used in this section will all be molar concentrations, because in homogeneous solutions active mass is the ratio of amount of substance to unit volume. Molar concentration will be indicated by c, with the solute in parenthesis following the symbol, or by placing the solute molecule or ion symbol in square brackets. Other concentration units, such as molality, are less commonly usedin aqueous equilibrium calculations.
Gases dissolve in liquids to form solutions.
This dissolution is an equilibrium process for which an equilibrium constant can be written. The form of the equilibrium constant shows that the concentration of a solute gas in a solution is directly proportional to the partial pressure of that gas above the solution. This statement, known as Henry's law , was first proposed in 1800 by J.W. Henry as an empirical law well before the development of our modern ideas of chemical equilibrium. In this form p is the partial pressure of the gas, c is its molar concentration, and k'c is the Henry's law constant on the molar concentration scale. Henry's law is found to be an accurate description of the behavior of gases dissolving in liquids when concentrations and partial pressures are reasonably low.