Einstein Science Reporting for Kids
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12-May-2005

Contact: Kenneth Klabunde
kenjk@k-state.edu
785-532-6849
Kansas State University

How fireworks work: The 'bang!' behind the beauty

MANHATTAN, KAN. --Fireworks light up the night sky on Independence Day and have become as much a part of the July 4 ritual as American flags and cookouts. But behind the scenes, causing those dazzling explosions, is a combination of oxygen, metals and a whole lot of innovation.

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.

Did you ever wonder what makes fireworks explode in a rainbow of colors? The answer: metals. When a metal burns, it emits photons that we see as light. Because different metals emit photons with different wavelengths as they burn, each metal produces its own individual color of light. So which metal makes which color?

Red - Strontium and lithium
Orange - Calcium
Gold - Incandescence of iron, charcoal or lampblack
Yellow - Sodium
Electric White - Magnesium or aluminum
Green - Barium plus a chlorine producer
Blue - Copper plus a chlorine producer
Purple - Strontium plus copper
Silver - Aluminum, titanium or magnesium powder or flakes

These metals can't do it alone. Most are in compound forms when burning in fireworks.

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Information from K-State distinguished professor of chemistry Kenneth Klabunde and http://chemistry.about.com/library/weekly/aa062701a.htm