quimica das coisas


Today, in “The Chemistry of Things”, we will get to know one of the most spectacular manifestations of chemistry in our lives. Who doesn’t get dazzled by the explosion of colours and shapes that light up the sky during a fireworks show!?

The essential component of fireworks the “shell”, usually a paper tube filled with black powder and small globes of explosive material called “stars”.

Each star contains four chemical ingredients: a combustible material, an oxidizing agent, a metallic compound responsible for the colour and  an agglutinant to keep these compounds together.

All light, colour and sound result of these chemical compounds. During the explosion, the oxidizing agent and fuel react violently releasing intense heat and materials in gaseous phase.

It is the sudden expansion of gaseous materials that creates a shock wave that reaches our ears, as the sound of the explosion!

And the heat released in this reaction is responsible for the brightness and colour of fireworks!

The colours of fireworks are obtained essentially by a process called “luminescence “.  The heat released in the blast is absorbed by the atoms of the metals present in the composition of the “star”. By absorbing energy, the atoms in the metals get their electrons a bit “messy”, let’s say, out of their usual positions!

When once again they arrange the electrons in their more stable positions, atoms release the excess energy, but now in the form of visible radiation, or coloured light.

The colour of the light varies according to the metal that is used: red is normally obtained with strontium salts or lithium;  orange is characteristic of calcium salts such as calcium chloride; yellow comes from sodium salts, the most commonly used being sodium chloride (kitchen salt); green is obtained with barium chloride, while blue is associated with copper chloride.

The properties of these salts make pyrotechnics a demanding chemical science. It is necessary to ensure the stability of some of these compounds, strictly control the temperature of explosion and prevent contamination and mixing colours.

Only like this can we ensure the beauty of chemistry illuminating the night sky in celebration!