1. Gases Part 2

2. Effusion and Diffusion
Diffusion - spontaneous intermingling of the molecules of one gas
Effusion - gradual movement of gas molecules through a very tiny hole into a vacuum
RATES of both depend on speed of gas molecules
Faster the molecules move, more rapidly diffusion and effusion occur

3. Graham’s Law
Thomas Graham studied rates of diffusion and effusion of variety of gases
Sent through porous clay pots and small openings
At same T & P, found rates of effusion were inversely proportional to square roots of density

4. Graham’s Law DIFFUSION AND EFFUSION
Can compare by taking ratio of effusion rates
Also, can compare to molecular mass

5. Graham’s Law in Use
The hydrogen halide gases all have the same general formula, HX, where X can be Cl, Br, or I. If HCl(g) effuses 1.88 times more rapidly than one of the others, which hydrogen halide is the other, HBr or HI?
HX is 128 which corresponds to HI.

6. Kinetic-Molecular Theory
Gas consists of an extremely large number of very tiny particles that are in constant, random motion.
The gas particles themselves occupy a net volume so small in relation to the volume of their container that their contribution to the total volume can be ignored.
The particles often collide in perfect elastic collisions with themselves and with the walls of the container, and they move in straight lines between collisions neither attracting nor repelling each other!
In 19th century, wanted to know how gases “work”?
The Kinetic-Molecular theory is True for ALL Gases
Almost like a bunch of billiard balls rolling around and bouncing

7. Real Gases Gases do not obey gas laws.. Why? Van der Waals equation
Gas particles do have volume
Small forces of attraction
Van der Waals equation
Where V is correction to bring measure P up to the pressure an ideal gas would exert, n is the correction to reduce measured V to the volume an ideal gas would have, and a and b are van der Waal’s constant