Gas Laws

Submitted by ChemPRIME Staff on Thu, 12/16/2010 - 13:20

Toward the end of the eighteenth century, many scientists began studying the relationships between pressureForce per unit area; in gases arising from the force exerted by collisions of gas molecules with the wall of the container., temperatureA physical property that indicates whether one object can transfer thermal energy to another object., and volume for gases. They began to realize that relationships between these measurements were the same for all gases. Gases behave similarly to a good approximation over a wide range of conditions, due in part to the large space between gas molecules. Simple gas laws were devised to predict the behavior of most gases. These gas laws, now recognized as special cases of the The Ideal Gas Equation, describe the effect of pressure on volume (Boyle's Law), of temperature on volume or pressure (Charles's Law and Gay-Lussac's Law), and of amount (in mol) on volume (Avogadro's Law).

There are several videos on YouTube that show the effects that can be understood in terms of these laws, and help visualize the impact of the 14.7 lb/in2 of air pressure that we live under and seldom notice:

• In one, water is added to a 55 gallon drum and boiled, letting steam and air escape, so that the drum is filled with hot water vaporThe gaseous state of a substance that typically exists as a liquid or solid; a gas at a temperature near or below the boiling point of the corresponding liquid.; then the drum is sealed and cooled. The water condenses (because of it's high polarity, the molecules attract), and the drum collapses.

• This can be done on a small scale with a soda can.

or on a large scale:

• This actually happened to a railroad tanker car that was being steam cleaned!

If your workstation is subscribed to JCE Software, the following video demonstrates a consequence of the gas laws. A large metalAn element characterized by a glossy surface, high thermal and electrical conductivity, malleability, and ductility. drum is set up over a Meker burner. Enough water is added to the drum to cover the bottom of it. The water and drum are then heated until the water becomes a gas. The air inside the drum is also being heated, and as it expands much of it leaves the drum, being replaced by water vapor. As soon as the vapor cloud is seen coming out of the drum, it is sealed with a threaded cap and removed from the burner. It is then transferred to a cart filled with ice and quickly cooled, which causes condensationThe process in which a liquid forms from gas or vapor of the same substance. A chemical reaction in which two molecules combine to form a very small molecule and a larger molecule than either of the two reactants. of the water vapor within the can. The resulting change in pressure inside the can allows the atmospheric pressure to crush the drum within a few minutes, in spectacular fashion.