Fireworks

These colourful explosions are the hallmark of any grand celebration. The chemistry inside fireworks determine their colour, shape and size.

Fireworks are synonymous with celebrations. Whether you’re celebrating Chinese New Years, the 4th of July or Canada Day, each celebration features an awe-inspiring display of colour. The chemistry behind these fireworks date back to around 800 AD in ancient China and remains relatively unchanged today.

Fireworks are composed of four main components: fuel, oxidizer, binders and colouring agents. Gun powder acts as both the fuel and the oxidizer for fireworks. It consists of Potassium Nitrate, Sulphur and charcoal. Potassium Nitrate is the oxidizer for gun powder because it will decompose at high temperatures and release oxygen. This allows the gunpowder to combust without direct exposure to the atmosphere or while wet since it has its own source of oxygen. The Sulphur will undergo exothermic reactions which continually releases heat into the mixture after ignition. The charcoal is the material that will act as the fuel in the combustion reaction. Gunpowder has the three basic ingredients required for combustion reactions: Oxygen (Potassium Nitrate), fuel (charcoal) and heat (Sulphur). As gunpowder burns, it violently releases gas which propels the fireworks into the sky.

Now that we know how fireworks fly and explode, what gives fireworks their vibrant colours? Metals! Different metal colourants are added to fireworks depending on the desired colours. Metals are perfect for this application because they are stable and have discrete energy gaps. As metals are excited by the energy released from the combustion reaction, their valence electrons enter an excited state. As that electron returns to its ground state, the excess energy is released as light. Different metals have different energy gaps that are proportional to a given wavelength in the visible light spectrum. For example Strontium (Sr) releases red light, Calcium (Ca) releases orange light and Copper (Cu) releases blue light. Other metals such as Sodium (Na), Magnesium (Mg) and Barium (Ba) are used for other colours.

The last component of the firework are binders. Binders simply combine the metal colourants and gun powder into a stable mixture. Dextrin, which is a type of sugar, is typically used. All of these ingredients are combined in different proportions depending on the colour, size and shape of firework that is desired.

By adjusting the formulations, one can achieve any colour and size and produce a fantastic firework show. Next time you see fireworks, remember they are all exploding with the same basic chemical principles.