Fireworks originated in China about 2000 years ago. Gunpowder, also known as black powder to distinguish it from modern smokeless powder, is the earliest known chemical explosive. Nearly a thousand years later, a Chinese monk named Li Tian created the first firecracker by filling a bamboo stick with gunpowder and throwing it into a fire, creating a loud explosion.
Today, fireworks are used to celebrate events and traditions in many cultures around the world. Although the 4th of July is still the "big day," Americans use fireworks year-round to celebrate at festivals, special events, sporting events such as the Super Bowl and the famous Disney show. Fireworks lit up the sky across Japan to mark one year until the start of the Tokyo Olympics.
We're all a little obsessed with these breathtaking sights, but why do some fireworks explode, some whistle and others crackle? What creates the dazzling reds, oranges, yellows, greens, blues and purples that explode into the sky, eliciting "oohhhhs" and "ahhhhhhs" from captivated onlookers?
Delight budding fireworks engineers in science class by showing them the chemistry behind the beautiful colors and deafening sounds of fireworks that ignite our emotions.
First, let's look at some of the science behind these dazzling symphonies in the sky.
Explosive combination
Every firework contains at least one oxygen-rich chemical, an oxidizing agent:
- Potassium nitrate
- Potassium perchlorate
- Strontium nitrate is rich in oxygen, but also produces a red flame
You then need fuel to combine with the oxidizer to produce heat. Substances such as sulfur, charcoal, aluminum or magnesium powder are used as fuel. The oxidizer breaks down the chemical bonds in the fuel, releasing energy. Fire (from a wick or direct flame) starts a chemical reaction.
What lies behind the sounds of clicks, crackles and explosions
Cover your ears! When some fireworks go off, they can rival the loudest thunderstorm.
The chemical mixture contained in a firework determines the sound it makes. Pyrotechnicians burn this mixture to create the explosion or blast that we look forward to when fireworks go off. Gunpowder is a bursting charge made from sulfur, charcoal and potassium nitrate (saltpeter). Sulfur and charcoal act as fuels, while saltpeter is an oxidizing agent.
There are more modern explosive charges with metal powder inside that are sharper and louder and flash with a light effect, creating fireworks that shake the house. Common bursting charges include:
- Black powder
- Flash of gunpowder
- H3
- Mix of whistles
Keep your powder dry because once the fuse is lit, it burns in the center of the case, ignites the time-delay fuse connected to the bursting charge, and BOOM!
That booming sound we hear after an explosion is caused by the rapid release of energy, which causes the air to expand faster than the speed of sound, creating a shock wave. Those shells exploding in the air are surely proof that our flag is still there (play patriotic music here)!
How Fireworks Get These Spectacular Colors
We know that various chemical elements, when heated to high temperatures, get rid of this energy by emitting specific wavelengths of light. Metal salts are ideal for fireworks because these compounds produce intense colors when burned.
Some examples include
- Strontium for red
- Barium for green
- Calcium for orange
- Copper for blue
- Sodium for yellow
- Copper and strontium for violet
When an element is ignited, the electrons surrounding the atoms are excited and charged with energy in the flame. When different elements ignite, they emit different wavelengths of light, which are converted into different colors depending on the type of fireworks.
Some colors are more difficult to reproduce than others. Most pyrotechnic engineers agree that blue is the most difficult color to produce. This is because the evening sky has a tint of blue, so most blue hues don't show up as well as other colors. If you try to brighten the blue to contrast with the background, it may look washed out. You must get the right balance of copper and other chemicals in the flame or combustion reaction to get the best blue flame in your fireworks.
Students will enjoy learning about the chemistry of pyrotechnics. One day they may become the pyrotechnician who delights us with the roar, pops and bright colors of fireworks.
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