# Daltons Law of Partial Pressures and Gay-Lussac’s Law

## Daltons Law of Partial Pressures:

Dalton (1801) observed that if two or more gases that do not react chemically are enclosed in a vessel, the total pressure exerted by the gaseous mixture is the sum of partial pressures of the individual gases. The partial pressure of a gas in the gaseous mixture is the pressure that the gas would exert if it were alone in the vessel. Mathematically, Dalton’s law of partial pressures may be stated as under-

Where ‘P’ is the total pressure exerted by the gaseous mixture and p1, p2, p3, etc. are the partial pressures of the components. In the case of moist gas, the pressure exerted by it is equal to the sum of the partial pressure of dry gas and partial pressure of water vapour it holds, known as aqueous tension. Thus, the pressure of the dry gas can be obtained by subtracting an aqueous tension from the pressure of the moist gas. The aqueous tension is definite for each temperature.

## Gay-Lussac’s Law (Law of Combining Volumes of Gases):

According to this law, when gases react, the volumes of the reactants and products (if gaseous) bear a simple ratio to one another. All volumes being measured under the same conditions of temperature and pressure.

For example- 1 volume of H2 combines with 1 volume of Cl2 to form 2 volumes of Hydrogen chloride.

Similarly we have-