Henry's Law - Formula and The Henry's Law Constant

Formula and The Henry's Law Constant

Henry's law can be put into mathematical terms (at constant temperature) as

where p is the partial pressure of the solute in the gas above the solution, c is the concentration of the solute and k_H is a constant with the dimensions of pressure divided by concentration. The constant, known as the Henry's law constant, depends on the solute, the solvent and the temperature.

Some values for k_H for gases dissolved in water at 298 K include:

oxygen (O₂) : 769.2 L·atm/mol

carbon dioxide (CO₂) : 29.41 L·atm/mol

hydrogen (H₂) : 1282.1 L·atm/mol

There are other forms of Henry's Law, each of which defines the constant k_H differently and requires different dimensional units. In particular, the "concentration" of the solute in solution may also be expressed as a mole fraction or as a molality.