THE CHEMISTRY OF

FIREWORKS

Where it all began

The discovery of fireworks is believed to have occurred approximately 2,000 years ago in China.

It is thought that a Chinese cook accidentally mixed three common kitchen ingredients…

These were heated over a fire and dried to give a black flaky powder which burned with a loud bang when ignited. This crude, early mixture has come to be known in our modern world today as gun powder.

SULFUR CHARCOALKNO3

ITEM OF PEACE OR WAR? (1)

Within 100 years the Chinese had developed fire arrows and other such firearms from the explosive.

Roger Bacon an English Scholar realized that Salt Peter (KNO3) was the key to the explosive power.

In 1560, European Chemists made gunpowder as explosive as possible by developing a new kind of ratio proportion…

The final proportion was set as follows:These ratios are still used today after 500 years

It was the Italians who made Fireworks what they are today

Aerial shells that launched upward and exploded into a fountain of color, lighting up the night sky

SULFUR10%

CHARCOAL15%

‘Saltpeter’

KNO375%

ITEM OF PEACE OR WAR? (2)

The evolution of Fireworks

For nearly 2,000 years, the only colours fireworks could produce were yellows and oranges

Using steel and charcoal.

In the 19th Century, pyro-technicians developed the technology to introduce reds, greens and blues to the firework displays

What’s inside a Firework?

Theory of Combustion

The Chemistry of fireworks is based on the theory of combustion:

Combustion is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame.

The composition inside the firework must however contain 6 vital ingredients…

OxidizingAgent

ReducingAgent

Fuel

Binder

ColoringAgent

Regulator

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Firework Fuel (1)

Normally, all fuels will contain an organic element such as charcoal or thermite. Charcoal (a.k.a. black powder) is the most common fuel used in fireworks.

The fuel loses electrons to atoms within the oxidiser (thereby reducing the oxidiser) and releasing atoms from the oxidiser.

During this process, bonds are formed between the fuel and oxygen atoms forming a product which is relatively stable.

Firework Fuel (2)

Only a minimal amount of energy is required to start the combustion of this fuel-oxidiser compound.

When combustion does start, the result is a massive release of energy as the solid mixture liquefies and vaporizes into the flame of ignition.

This maximizes the probability of reaction of the oxidizer as it is brought into the close proximity of the flame. BACK

Oxidising Agents (1)

The function of the oxidising agent is to produce the oxygen needed in order for the mixture inside the firework to burn.

These oxidisers can be nitrates, chlorates or perchlorates.

XNO3 XNO2+ ½ O2

Oxidising Agents (2)

Nitrates only give up a third of their oxygen as the equation above illustrates.

Chlorates get completely reduced as they are better oxidising agents and so cause an even more spectacular reaction.

2XClO3 2XCl + 3O2

Oxidising Agents (3)

Perchlorates contain even more oxygen but are less likely to explode than chlorates due to their increase in stability.

They follow the reaction below:

XClO4 XCl + 2O2

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Reducing Agent

These burn the oxygen provided by the oxidising agents to produce hot gasses.

Common reducing agents are Sulphur and Charcoal.

These react with the oxygen to form Sulphur dioxide and Carbon dioxide respectively: S+O2 - SO2

C+O2 - CO2

Regulators

Metals can be added to regulate the speed at which the reaction. The larger the surface area of the metal, the faster the reaction will proceed (collision theory).

By mixing both the reducing agents, the speed of the reaction can be controlled.

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Colouring Agents (1)

Different chemicals are used to produce different coloured fireworks.

In order to produce a firework of a certain colour, the correct corresponding chemical or as the case may be, mixture of chemicals can be used.

The incandescence from the elements occurs when solid particles are heated in the flame to extremely high temperatures. These release excess energy in the form of light (hv) at the broad end of the spectrum.

Colouring Agents (2)

Metal StrontiumCopper BariumSodiumCalciumIronStrontium + Copper

ColourRedBlueGreenYellow/OrangeOrangeGoldPurple

Colouring Agents (3)

The incandescence from the elements occurs when solid particles are heated in the flame to extremely high temperatures.

These release excess energy in the form of light (hv) at the broad end of the spectrum.

The higher the temperature, the shorter the wavelength at which light is emitted, and the nearer it tends toward the blue end of the coloured spectrum.

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BINDERSBinders are used to hold what is essentially the mixture of the firework together in a paste like mixture.

The most commonly used binder is known as dextrin.

The binders do not actually begin to work until the firework has been lit as they are too unstable for storage within the firework and are hence potentially dangerous. BACK

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