1. Macroscopic Properties of Gases
expand to fill the volume of any container
have much lower densities than solids or liquids
have highly variable densities, depending on conditions
mix with one another readily and thoroughly
change volume dramatically with changing temperature

2. Pressure
If a force of magnitude F is applied to a surface with an area equal to A, then we say that the pressure on that surface is P and is given by

3. Pressure of a Gas in a Container
Pressure of a gas in a container results from molecular collisions of gas molecules and container walls.
Each collision imparts a small amount of force.
Summation of the forces of all molecular collisions produces the macroscopic property of pressure.

4. Atmospheric Pressure
The height of the mercury column is proportional to atmospheric pressure.

5. Charles’s Law

6. Postulates of Kinetic Molecular Model
a) Gases are made up of large collections of particles, which are in constant, random motion
b) Gas particles are infinitely small and occupy negligible volume
c) Gas particles move in straight lines except when they collide with other particles or with the container walls. These collisions are elastic, so kinetic energy of particles is conserved
d) Particles interact with each other only when collisions occur
e) The average kinetic energy of a gas is proportional to the absolute temperature of the gas but does not depend upon the identity of the gas