How do Fireworks Work? A Chemistry Lesson
This Independence Day after you’ve finished your extra helpings of hot dogs, casseroles, and side salads, and you're settling in next to the fire to make s’mores and watch fireworks, someone will be bound to ask, “How do fireworks work?”
Well, this year we’ve got you covered.
We brought in an expert to help answer some of the trickier chemistry questions — who better than chair and associate professor of chemistry here at D’Youville, Dr. Dominic Ventura, to make sure you’re ready with all the firework chemistry answers you’ll need.
We asked Ventura to start with the basics: how fireworks work and where they get their colors.
"Everything needed to create the different lights, colors, and sounds of a firework are located inside of a shell. The firework launches from inside of a tube into the air due to lighting a lift charge. This works the same way as firing a cannon or an old-timey musket,” Ventura says, when asked about the basics of fireworks.
For the most part, the larger the shell the higher they’ll go. And the explosion from the lift charge that launches the firework into the sky also lights another fuse attached to the shell. This fuse is on a delay to give the firework time to get higher into the air before exploding into a burst of color and sound.
“The shell is usually filled with gunpowder or some other explosive agent, called a burst charge, which, you may have guessed, explodes when it’s lit,” Ventura adds.
Inside of the shell, along the burst charge, are little pellets called stars. Each of these stars contain different compounds and metals and once they’re ignited, they all burn a little differently.
“[The color] all depends on the metal being burned inside the firework,” says Ventura, when asked about the color of fireworks. “For the most part, these metals are found in Group 2 of the Periodic Table of elements — alkaline earth metals such as calcium, barium, and strontium release their energy by producing different wavelengths of light.”
The Periodic Table of Elements with Group 2 — alkaline earth metals, aka fun firework metals — outlined in red.
While you may still be pondering how your great-aunt Agnes got the potato salad you ate earlier to be so yellow, you should know now that the yellow firework that just went off above you was because of the sodium salts burning away.
The temperature also has a big impact on color. “The hotter the temperature that the firework burns at, the brighter the color. But if it gets too hot, the metals that emit those colors will be destroyed,” adds Ventura.
As the firework show goes on, you may have noticed that you don’t see many blue fireworks. While it’s easy enough to light copper salts to create that blue color, the metals get destroyed easily at higher temperatures.
“You never really see those bright, brilliant blues because it’s hard to get the copper to hot enough temperature that it doesn’t blend in with the night sky,” Ventura says.
As they burn, certain metals emit different colors. Caution: Contents may be hot.
We all have a favorite firework, and for Ventura, those are “the big white ones that give the loud boom — those ones that you can feel.” So now we know that it’s magnesium or aluminum that’s burning to create the white color, but what makes some fireworks louder than others?
Ventura says it comes down to a few things, including how fast the chemical reaction is: “The faster the reaction, the louder the boom.”
Enclosing fast-reacting chemicals inside a tiny shell creates a loud boom because the gases expand faster than the speed of sound, while using slow-reacting chemicals can create whistling effects.
“The crackling noise you’ll hear is the vaporizing of lead atoms. The whistling comes down to how wide or narrow the tube that carries the firework is,” says Ventura.
What about the cool shapes that fireworks make? Remember the little pellets inside of the shell? Their placement is usually pretty specific. How they’re stacked and spaced from the center of the burst charge eventually leads to different shapes as the explosion of the charge will send the stars off into all the different patterns we’ve come to love.
It’s the pyrotechnic chemists that get creative with different combinations of patterns, number of shells and fuses, and metals to create the shows that wow us.
As you look towards the sky on Independence Day, or Canada Day for our friends up North, and hear the sounds of “Ooh,” “Aah,” and “That one was cool,” feel free to bring a little chemistry knowledge to your fellow onlookers.