Dalton's law of partial pressure

Dalton proposed this law on the pressure exerted by a mixture of non-reacting gases in an enclosed vessel. The law of partial pressure states that the total pressure exerted by a mixture of two or more non-reacting gases in a definite volume is equal to the sum of the individual pressures, which each gas would exert if it occupies the same volume at a constant temperature. If p₁, p₂, p₃ are the individual partial pressures of the known gases, then the total pressure 'P' of the mixture of gases at the same temperature and pressure is given by the relation:

P = p₁ + p₂ + p₃ + …….

Partial pressure is the pressure exerted by the gas if present alone in the vessel at the same conditions of temperature.

For example,

A gas 'A' having a pressure of 300 mm Hg is contained in a vessel and another gas 'B' with a pressure of 400 mm Hg is contained in another vessel, are mixed in the third vessel at the same temperature. The total pressure in the third vessel is,

P = P_A + P_B

= 300 + 400 = 700 mm Hg

Fig: 2.5 - Dalton's law of partial pressures

Dalton's law is used to calculate the pressure of a gas.

Problem

3. A 10 L flask at 298 K contains a gaseous mixture of CO and CO₂ at a total pressure of 1520 mm of Hg. If 0.20 mole of CO is present, find the partial pressure of CO and that of CO₂?

Solution

According to Dalton's Law: p_CO + p_CO2 = P = 1520 mm of Hg

= 0.49 atm.

Partial pressure of CO₂, p_CO2= P - (p_CO)

= 2.0 - 0.49 = 1147.6 mm of Hg