Gases

A gas is any physical substance that must be contained in a sealed container or it will soon dissipate. These molecules have little attraction for each other and travel in a straight line (fly) and will ricochet or rebound from each other, from other molecules of any substance, or from the container walls. They have little or no attraction neither for each other nor for any other substance.

Any particular substance can be made to exist in any of these three forms; that is, it may exist as a solid, a liquid, or a gas. Any molecule can be made to vibrate, swim, or fly depending on two things temperature and pressure. To understand this change of state, one must study temperature and pressure relationships.