The Chemistry Behind Fireworks

By Darryl Ho 4L04

What is a firework ? What are fireworks made of ? The chemistry behind fireworks Stage 1 : Redox Reaction Stage 2 : Excitement of electrons Effect : Different metals, Different colours

Content

What is a Firework ?

It is a low explosive pyrotechnic device used primarily for special effects and entertainment

purposes.

Oxidising Agent Firework Rocket Fuel Gunpowder Colouring Agent Binder

What is a Firework Made Of ?

Stage I

Lift Off

STAGE I - The Lift Off

Redox reactionRedox reactionbetween the oxidising between the oxidising agents and the rocket fuelagents and the rocket fuel

Thermal decomposition of oxidising agents Oxidising Agents used: KNO3, KClO4, KClO3

Potassium nitrate is reduced into potassium oxide and nitrogen gas as it loses oxygen.

Thus reduction of potassium nitrate takes place and oxygen gas is produced.

STAGE I - Redox Reaction

4 KNO3 4 K2O + 2N2 + 5 O 2

Oxidation of rocket fuel Rocket Fuel: Carbon + Sulphur Powder Sulphur and carbon reacts with the oxygen provided by

the reduction of oxidising agents to form sulphur dioxide and carbon dioxide respectively

Both sulphur and carbon are oxidised to gain oxygen, forming large amounts of sulphur dioxide and carbon dioxide as products.

STAGE I - Redox Reaction

O (g) + S(s) S O (g) 2

O (g) + C(s) C O (g) 2

2

2

Large volumes of carbon dioxide and sulfur dioxide gases are formed.

They exert a force on the ground due to high pressure in the rocket, creating

an upward thrust on the rocket.

This lifts the rocket into the air.

The Result

STAGE II – Excitement of Electrons

Excitement of electrons of metal atoms

STAGE II - Heating of Colouring Agents

Coloring agents used are salts of metals or their compounds.

The metal atoms or cations absorb the thermal energy produced by the combustion of sulfur and carbon powder.

The thermal energy that is absorbed causes the electrons of the atom from the lowest energy state to become excited and enter the highest energy state of an atom, called an excited state.

The excess energy of the excited state is released as the electrons descend to lower energy states.

The energy released is emitted as light energy in the process.

STAGE II - Heating of Colouring Agents

The End Result

Effect - Different Metals ………. Different Colours The electrons of different metals release different

amount of energy when excited and produce an electromagnetic wave of a particular wavelength.

Hence, different metals produce different colors of light when burnt.

Higher Energy

Lower Energy

Shorter Wavelengths

Higher Wavelengths

Effect - Different Metals ……….Different Colours

COLOUR CHEMICAL WAVELENGTH

Red Lithium Salts 650 nm

Orange Calcium Salts Calcium (II) Chloride

670 nm

Yellow Sodium Salts Sodium Chloride

610 nm

Blue Copper(I) Chloride 535 nm

Silver Magnesium, Aluminium

and Titanium Salts

The End. Thank You.