Lecture 14.4- Diffusion (HONORS)

Chemistry 14.4

Bellwork- Ideal Gas Law

How many moles of oxygen gas are in a balloon at 25C with an internal pressure of 1.1 atm and a volume of 1500ml?

P1V1 P2V2 PV = nRT

T1 T2 R= 8.31 LkPa/Kmol

R= 0.0821 Latm/Kmol

=

A list of gear for an expedition to Mount Everest includes climbing equipment, ski goggles, a down parka with a hood, and most importantly compressed-gas cylinders of oxygen. You will find out why a supply of oxygen is essential at higher altitudes.

The contribution each gas in a mixture makes to the total pressure is called the partial pressure exerted by that gas.

Dalton’s law of partial pressures- In a mixture of gases, the total pressure is the sum of the partial pressures of the gases.

Three gases are combined in container T.

100 kPa + 250kPa + 200kPa = 550kPa

The partial pressure of oxygen must be 10.67 kPa or higher to support respiration in humans. The climber below needs an oxygen mask and a cylinder of compressed oxygen to survive.

Atmospheric pressure at the top of the world (29,000ft above sea level)

= 30kPa

14.6

14.6

14.6

14.6

for Sample Problem 14.6

Diffusion is the tendency of molecules to move toward areas of lower concentration until the concentration is uniform throughout.

Graham’s Law

Bromine vapor is diffusing upward through the air in a graduated cylinder.

Graham’s Law

After several hours, the bromine has diffused almost to the top of the cylinder.

During effusion, a gas escapes into a vacuum through a tiny hole in its container.

QuickTime™ and a decompressor

are needed to see this picture.

Gases of lower molar mass diffuse and effuse faster than gases of higher molar mass.

Graham’s law of effusion states that the rate of effusion of a gas is inversely proportional to the square root of the gas’s molar mass. This law can also be applied to the diffusion of gases.

KE = ½ massvelocity2

Two gases at the same temperature have equal kinetic energy, but their masses are different. HEAVIER = SLOWER

A helium filled balloon will deflate sooner than an air-filled balloon.

Helium atoms are less massive than oxygen or nitrogen molecules. So the molecules in air move more slowly than helium atoms with the same kinetic energy.

Because the rate of effusion is related only to a particle’s speed, Graham’s law can be written as follows for two gases, A and B.

Helium effuses (and diffuses) nearly three times faster than nitrogen at the same temperature.