New Year’s Eve transforms the sky into an open-air laboratory. Lights burst into shapes, colours mix, crackle and fade in a fraction of a second. What we perceive as a celebration is in fact a precisely controlled sequence of chemical reactions – fast, energetic and visually impressive. Fireworks are not chaos. They are the result of carefully designed chemistry, in which each component has its own role.
Metal salts are the basis of colour effects in fireworks. When burned, their atoms become excited – they absorb energy and their electrons move to higher energy levels. When the electrons return, they release energy in the form of light. It is the differences in the energy levels of the individual elements that determine the colour we see. Strontium compounds produce an intense red colour because their atoms emit light with a characteristic wavelength in the red region of the spectrum. Copper, on the other hand, produces blue and blue-green tones, sodium is responsible for yellow light, and barium for green hues. The colour of fireworks is therefore not the result of dye in the usual sense of the word, but a manifestation of the atomic structure of a particular element. Interestingly, the purity of the colour depends on the exact composition of the mixture and the burning temperature. Too high a temperature can “burn” the colour and weaken it, while too low a temperature cannot excite the atoms sufficiently. The chemist who designs fireworks therefore works with the same precision as a laboratory technician in a spectroscopic laboratory.
In order for colours to appear in the sky, energy must be released. This is provided by explosive or highly combustible mixtures that form the energetic core of fireworks. Typically, this is a combination of fuel and an oxidising agent.
When ignited, a rapid oxidation-reduction reaction takes place. The fuel oxidises, the oxidising agent reduces, and a large amount of heat and gases are released. It is the expansion of the gases that causes the flare to shoot upwards and then “break up” into individual coloured dots.
The important thing is that this is a controlled explosion. The reaction speed, particle size and ratio of components are precisely adjusted so that the energy is not destructive, but visually effective.
The colourful effect of fireworks is short-lived because the excited atoms quickly return to their ground state. The light we see is just a moment of energy release. When the fuel is exhausted and the temperature drops, the process ends. All that remains is smoke – a mixture of solid particles and gases, which are a less poetic but inseparable consequence of the reaction. This is one of the reasons why the New Year’s Eve sky is always temporary. The chemical reactions that light it up are fast, one-off and irreversible.
In addition to their beauty, fireworks also have a less visible side. The smoke they leave behind contains fine dust particles, metal residues and combustion products. These substances can temporarily worsen air quality. The metal particles that create the colours settle back to the ground after the explosion and can get into the soil or water.
That is why there has been increasing discussion in recent years about more environmentally friendly alternatives – fireworks with lower toxic metal content, quieter versions, or light and laser shows that can create a similar visual effect without smoke.
New Year’s Eve is a night when abstract concepts from textbooks – atoms, electrons, oxidation-reduction reactions – are transformed into colours, sounds and emotions. The colourful alchemy of fireworks shows that chemistry does not have to be hidden in test tubes. It can be right above our heads. And although it only lasts a few seconds, its principles are precise, verifiable and fascinating.
Ing. Mária Zajičková, PhD.
organic chemist, science populariser
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