(Kinetic Molecular Theory) KMT (Kinetic Molecular Theory) Particle Size 1. Gases consist of tiny (submicroscopic) particles. The distance between particles is large compared with the size of the particles themselves. The volume occupied by a gas consists mostly of empty space. Particle Motion 3. Gas particles have no attraction for one another. Gas particles move in a straight line in all directions, colliding frequently with one another and with the walls of the container. Particle Energy No energy is lost by the collision of a gas particle with another gas particle or with the walls of the container. All collisions are perfectly elastic. 6. The average kinetic energy for particles is the same for all gases at the same temperature, and its value is directly proportional to the Kelvin temperature.

Pressure = Force Area 1 atm Units of Pressure: 760 mm Hg # of collisions & speed of collisions 1 atm Units of Pressure: 760 mm Hg (Table 12.1 pg 407) 760 torr 101.3 kPa 1013 mbar 14.7 psi 29.9 in Hg

Practice Problem Given unit New unit = New unit Given unit 1.12 atm A barometer reads 1.12 atm. Calculate the corresponding pressure in (a) mm Hg and (b) kPa. Given unit New unit = New unit Given unit 1.12 atm 760 mm Hg = mm Hg 851 1 atm 1.12 atm 101.3 kPa = kPa 113 1 atm

Dalton’s Law of Partial Pressures The total pressure of a mixture of gases is the sum of the partial pressures exerted by each of the gases in the mixture. PTotal = P1 + P2 + P3 … = Σ Pn Each gas exerts a pressure that is independent of the others.

An application of Dalton’s law is seen in the collection of gas by water displacement. PTotal = P1 + P2 + P3 … Patm = Pgas(es) + PH2O

Vapor Pressure of Water @ various Temperatures

What would be the partial pressure of N2 gas collected over water at 20oC and 720. torr? Patm = PN2 + PH2O @ 20oC PH2O = 17.5 torr 720. torr = PN2 + 17.5 torr 720. torr - 17.5 torr = PN2 = 702.5 torr = 703 torr