Henry's law equation(Henry's law) Formula

Definition: The Henry's law is used for describing a gas behavior. The law states that "At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid." This law was proposed by William Henry in 103 and it is used for determining the quantity of gases dissolved in water and a second way to define is that the gas solubility in a liquid is proportional to the partial pressure of the gas above that liquid.

Formula: The both ways to define this law can be expressed by the equation:

C = k P_gas

Where, C is the solubility of the gas at a certain temperature in a particular solvent and the units are M or gas/L. the constant k is te Henry's law constant and P_gas is the partial pressure of the gas.

Uses: The Henry's law is very useful in geochemistry, where it is used for calculated concentration of gases in mines. It is also useful for calculating a wide range of solutes when prepared solution near to the infinite dilution. Furthermore, environmental chemists use for calculating concentration of the gases in oceans and lakes.

Example: Calculate the Henry's constant for helium dissolved in water, the concentration of neon is 1,2 M and the pressure is 0.5 atm.

k = C P_He = 1.2M x 0.5 atm = 0.6 M atm^-1

In general, the concentration is expressed in M (mol L^-1) and the pressure in atmosphere, resulting in M atm^-1 in the units of the Henry's constant.

Considerations: It should be consider that the Henry's law is for applying only when the molecules are reached the equilibrium. Also, gases at a high pressure do not follow the Henry's law or if the solvent and solute reacts.