1. Gases Lecture 4
Diffusion & Effusion

2. Diffusion
the gradual, spontaneous mixing of gases due to the positive change in entropy associated with the process
Remember the cloud of chlorine gas floating around the room

3. Effusion
process of gas molecules confined in a container with a hole in it passing through that hole spontaneously
Two gases at the same temperature have the same kinetic energy
remember that temperature is a measure of kinetic energy
KE= ½ mv2
if KEA=KEB, then. . .
½ mAvA2 = ½ mBvB2
mAvA2 = mBvB2

4. another way of writing this equation would be. . .
vA/vB = mB/mA
because the rate of effusion depends only on the velocity at which the molecules in a gas are moving, the equation can be rewritten as. . .
rate of effusion of A mB =
rate of effusion of B mA
the lower the mass of a gas, the faster the rate of effusion
refer to page 388 of your book to see an example of an effusion problem