Spatial Equilibrium (or Nature Abhors a Vacuum)

1. Gas molecules are in continual motion. They move in a straight line until they collide with another molecule or with the walls of their container (also made of atoms and molecules). When molecules collide, they rebound with 100% elasticity.
2. Air is made of colliding gas molecules and odors are also made of gas molecules. If some odor is released from a container then the molecules will mix with molecules in the air. The multiple random collisions will cause the odor molecules to diffuse [spread randomly in all directions] into the surroundings.
3. The random motion of atoms as they jostled around by other atoms is called "Brownian Motion".
4. After the model is allowed to run for some time the gas molecules will reach a dynamic equilibrium.
5. A state of dynamic equilibrium occurs when measurements on a system are constant even though individual parts of the system are rapidly changing. For example, imagine two sets of people on opposite sides of a bridge. They begin to walk across in such a way that for every person who crosses from side A to side B, one crosses from side B to A. If you were to measure how many people are on either side of the bridge you would always get the same number. However, the specific people are always changing. This is a state of dynamic equilibrium.
6. Spatial equilibrium occurs when the average number of molecules of a particular kind found in a specific volume is unchanging.
7. For simplicity all gasses will be modeled as if they are made from single atoms. While true of some gasses (the ones in the Noble gas column of the periodic table), this is not true of other gasses at room temperature.