1. Dalton’s law of partial pressure At constant volume and temperature, the total pressure of a mixture of gases is the sum of the partial pressures of all the gases present. P total = P 1 + P 2 + P 3 …

2. Example What is the partial pressure of O 2 (P O2 ) at 1 atm if P N2 = 593.4 mm Hg, P CO2 = 0.3 mm Hg, and P others = 7.1 mm Hg?

3. Determine the total pressure of a gas mixture that contains O 2, N 2, and He if P O2 = 150 mmHg, P N2 = 350 mm Hg, P He = 200 mm Hg.

4. Mole Fraction and Partial Pressures Mole Fraction – a dimensionless quantity that expresses the ratio of moles of one component to moles of all components present. P a =  a P t, where  a is the mole fraction: mol A = X Total Moles