kinetic+molecular+theory

The physical properties of gases had become well known in Robert Boyle's time (1600's) and were eventually summarized in the Kinetic Molecular Theory (KMT), which even today is being used and modified.

The basic postulates of this theory outline the behaviors of an **//ideal gas//**, which behaves perfectly (this never happens, of course).
 * 1) Gas molecules are extremely small particles - so small, in fact, that their atomic or molecular volumes are considered to be negligible (zero) compared to the volume of their container.
 * 2) Gas molecules move quickly, and are extremely far apart, when compared to those in liquids or solids.
 * 3) Gas molecules undergo collisions (with surfaces and with one another) that exert a net force (this is the definition of gas pressure). They exchange energy during these collisions.
 * 4) Gas molecules do not interact with surfaces or with one another - their collisions are 'elastic', resulting in no net loss of energy.
 * 5) Gas molecules have a certain average kinetic energy - a mass-speed relationship (definition of gas temperature). Lighter gases move faster than heavier gases when at the same temperature.



Of course, no gas ever behaves ideally, so they do interact with one another (or with surfaces) during collisions, and they do actually have particular volumes. But for theory's sake these minor behavioral issues are ignored.

Other important properties of gases are:
 * they completely occupy their container
 * they can diffuse (travel) across a space
 * smaller molecules move faster than larger molecules at the same temperature
 * gases have different densities - carbon dioxide gas is very dense compared to helium gas

Worksheet:

Here is a video showing some neat properties of carbon dioxide gas, generated from dry ice in water. media type="custom" key="23657638"