June 26, 2004
Fireworks explosions begin at the molecular level, said Kenneth Klabunde, distinguished professor of chemistry at Kansas State University. Most metals are reactive with oxygen, which means they have a tendency to oxidize when exposed to air, he said. During oxidation, heat is released. The hotter it gets, the more reactive it becomes.
When a large chunk of a metal is exposed to oxygen, the outer surface oxidizes, protecting the inner metal from oxidation, Klabunde said. To avoid this, metals are ground into tiny particles before being packed into the firework. From there, it's all left to chemical reactions.
"It lights, goes up in the air, causes the rocket to blow apart and throws the metal into the air," Klabunde said. "When released, the metal particles start oxidizing and get so hot they give off light."
In more common fireworks, such as firecrackers or ladyfingers, that just create a flash of light and a loud pop, gunpowder comes into play.
"You want it to explode instantly, so you don't have time for air," Klabunde said.
Gunpowder, which is made of flammable materials such as carbon or coal, provides the needed oxygen for the oxidation of the metal particles, he said. The molecules have excess oxygen and become unstable if heated or jarred. When the fuse is lit, the molecules become unstable and give off oxygen that, in turn, reacts with the small metal particles, resulting in an explosion.
"You have two molecules that thermodynamically want to react," Klabunde said. "You just have to jar them, light a fuse or give them an electric shock."
Because the metals react with oxygen, fireworks lose their effectiveness when stored over long periods of time.
"Over time, oxygen from the air leaks in and slowly causes degradation," Klabunde said. To avoid this, fireworks are often stored under nitrogen or argon before distribution, he said.
But oxidation reactions occur in more than just fireworks -- they even occur in the human body. When people breathe, the oxygen from the air is used for chemical reactions in the body.
"We breathe in oxygen and breathe out carbon dioxide," he said. "We are oxidizing the food we eat."
Oxidation reactions are also what make TNT explode and the space shuttle take off.
"Our civilization has
learned to handle compound materials quite well even though we
live in a sea of oxygen," Klabunde said.
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