Dalton's Law of Partial Pressure

Return to Chemistry Index Page

Dalton's Law of Partial Pressure is the relationship between individual gasses in a gas mixture in that each gas makes up a part of the total pressure exerted by the gas mixture. Dalton's Law of Partial Pressure is written as P_T = P_{1  +} P_{2   +}  P_{3 .........}

Example Problem:

A sample of air contains  78 % Nitrogen, 21 % Oxygen, .97 % Argon and .0034 % of Carbon Dioxide what is the partial pressure each gas exerts in millimeters of mercury and what is the total pressure in millimeters of mercury?

 P_T = P_{1  +} P_{2   +}  P_{3 .........}

 There are 760 mm in 1 atm.

PT = N2 + O2 + Ar + CO2 .....

Partial Pressure in mm each individual gas exerts.

N2 is .78 x 760 mm = 592.8 mm

O2 is .21 x 760 mm = 159.6 mm

Ar is .0097 x 760 mm = 7.372 mm

CO2 is .00034 x 760 mm = 0.2584 mm

Total Pressure in mm exerted by all gasses in the mixture combined.

PT = 592.8 mm + 159.6 mm + 7.372 mm + 0.2584 mm = 760 mm total pressure