# Chemistry: Gay-Lussac's Law: Spray Paint + Campfire = Bad News

## Gay-Lussac's Law: Spray Paint + Campfire = Bad News

Back in 1802, Joseph Gay-Lussac read a story in the newspaper about a guy who threw a can of spray paint into a campfire. (Editor's note: Only the year in the preceding statement is true.) The unfortunate camper had apparently told his friends that he "wanted to see what would happen" immediately before the accident that claimed his life.

Gay-Lussac knew from the information on the sides of the cans that they shouldn't be stored at high temperatures, but he wanted to know the reason why it was such a bad idea. After a great deal of research, he came up with the following relationship, now known as Gay-Lussac's Law:

• P1T1 = P2T2
##### The Mole Says

The spray can example in this section assumes that the liquid inside of the can plays an insignificant role in how it behaves while being heated in the campfire. Though the liquid would probably vaporize, we'll assume it doesn't for simplicity's sake.

P1 is the initial pressure of a gas, T1 is the initial temperature (in Kelvin), P2 is the final pressure of a gas, and T2 both the volume of the gas and number of moles of gas is constant. If a spray can has an initial pressure of 1.50 atm and an intial temperature of 25º C (298 K), we can compute the internal pressure of the can when the gas inside has reached the temperature of a campfire (500º C, or 773 K):

• 1.50atm⁄298K = x773 K
• x = 4.25 atm
##### The Mole Says

Problem 2: Propane tanks can contain an internal pressure of 35.0 atm before bursting. If the tanks initially hold 20.0 atm of propane at a temperature of 20º, what is the maximum temperature they can reach before exploding?

From this, Gay-Lussac determined that the increased pressure inside the spray can caused the can to explode in the fire. Because spray cans contain flammable liquids and gases, a huge fireball was created when the can exploded.

Excerpted from The Complete Idiot's Guide to Chemistry © 2003 by Ian Guch. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin Group (USA) Inc.

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