Dalton’s Law of Partial Pressures

• In a mixture of non-reacting gases– Each gas particle behaves independently– Particles spread themselves out to occupy

the space available• According to the KMT, pressure is

caused by collisions with the walls of the container

Dalton’s Law of Partial Pressures

The total pressure of a mixture of non-reacting gases is equal to the sum of the partial pressures of the individual gases.

Ptot = P1 + P2 + P3 + …

Partial Pressures of Atmospheric Gases

• Air consists of a mixture of gases:N2 = 78.08% O2 = 20.95%

Ar = 0.93 %CO2 = 0.03%

If Standard atmospheric pressure is 101.3 kPa, determine the partial pressure of each gas.

Gas Collection over Water

• Gases can be collected by bubbling them through water.

• The gas collected is a mixture of the desired gas and water.

• To find the partial pressure of the desired gas, the vapour pressure of water must be subtracted.

Gas Collection over WaterHydrogen gas from the reaction of Zinc with hydrochloric acid

was collected by the displacement of water. Atmospheric conditions were 100.5 kPa and 20˚C.

Determine the partial pressure of hydrogen gas.

Ptot = Patm = PH2 + PH2O

PH2 = Patm - PH2O

= 100.5 kPa - 2.3 kPa

= 98.2 kPa

Homework

• Read p. 460-465• P. 461 #1-3• P. 463 #5• P. 465 #8-10; #1-7