The chemistry behind fireworks

However, behind their vibrant spectacle lies a fascinating mix of chemistry and physics. The creation of fireworks involves understanding the chemical reactions that produce light, color, sound, and smoke. The science behind fireworks can be broken down into several core components: the combustion reactions, the role of metal salts in color production, the propulsion of the fireworks, and the creation of sound effects.

1. Combustion Reactions: The Basis of Fireworks

At the heart of every firework is a chemical reaction known as combustion. Combustion is a process in which a substance (usually a fuel) reacts with oxygen to release energy, typically in the form of light, heat, and gas. In the case of fireworks, the fuel is usually a mixture of black powder (a form of gunpowder), which consists of potassium nitrate (KNO₃), charcoal (carbon), and sulfur (S). When ignited, the black powder undergoes a rapid oxidation reaction, producing a lot of heat and gas. This rapid release of energy results in an explosion that propels the firework into the air and creates an intense burst of light.

The specific chemical reaction for black powder is:

2 KNO

3

+

3 C

+

S

→

K

2

SO

4

+

3 CO

2

+

N

2

2 KNO

3

​

+3 C+S→K

2

​

SO

4

​

+3 CO

2

​

+N

2

​

The energy released by this reaction is responsible for the firework’s explosion, which creates the initial propulsion and subsequent display in the sky.

2. Color Production: The Role of Metal Salts

The vibrant colors seen in fireworks are one of their most captivating features, and they are the result of metal salts. When heated, different metal compounds emit specific wavelengths of light, creating the dazzling spectrum of colors. This phenomenon is due to the excitation of electrons in the metal atoms.

Strontium salts (like strontium carbonate) produce red colors. Strontium ions excite and emit light at wavelengths corresponding to red hues when they return to their ground state.

Copper compounds (such as copper chloride) are responsible for creating blue fireworks. Copper emits blue light when it is heated to high temperatures.

Sodium compounds (e.g., sodium nitrate) produce a bright yellow color. The energy transition of sodium ions emits light at the wavelength corresponding to yellow.

Barium salts (like barium chloride) produce a green color. When barium is heated, it emits green light.

Calcium compounds (such as calcium chloride) are used for orange colors, while magnesium and aluminum create white sparks due to their high-temperature emissions.

These metal salts are mixed with other ingredients in the firework shell, and when ignited, the heat causes the metal ions to emit light at specific wavelengths, producing the characteristic colors.

3. The Propulsion and Shell Design

Fireworks are typically contained in a shell that is designed to ensure a controlled explosion. The shell is made up of a combination of a propellant charge, the color-producing compounds, and stars (small pellets of explosive mixture). When the firework is lit, the black powder ignites and causes the shell to burst open at a certain height in the sky, creating the explosion.

The process of propulsion is achieved by the launching charge at the base of the firework, which ignites and produces gas at a rapid rate, propelling the firework upwards. The amount of charge used determines how high and how far the firework travels before it bursts.

Inside the shell, there are carefully arranged stars (small pellets of fuel mixed with metal salts) which explode upon ignition, creating the signature bursts of light. The shape and arrangement of these stars determine the pattern and form of the firework display.

4. Sound Effects: The Boom and Crackle

The loud noises produced by fireworks come from the rapid expansion of gases created during combustion. When the black powder or other explosive materials burn, they create a sudden release of energy that causes the air to compress and expand very quickly, generating sound waves.

The "bang" or "boom" is the result of a rapid release of gas when the shell bursts.

Crackling sounds are often produced by fireworks containing titanium or aluminum powder. These metals burn at high temperatures, producing small explosions that crackle in the air.

Other fireworks may produce different sound effects based on their composition, such as whistling or hissing sounds, which are created by adding specific materials like whistle mix (a combination of potassium perchlorate and sulfur) to the firework.

5. Safety and Environmental Considerations

The chemistry behind fireworks also raises important considerations for safety and environmental impact. The chemicals used in fireworks can be hazardous if not handled properly, both in the manufacturing process and during the display. Heavy metals, such as barium and strontium, can be toxic, and the pollution from fireworks can affect both air and water quality. The chemicals released into the air can also contribute to smog and particulate matter, leading to environmental concerns.

In recent years, efforts have been made to create more environmentally friendly fireworks, such as those that use less toxic chemicals and produce less smoke and fewer pollutants.

Conclusion

The chemistry behind fireworks is a captivating blend of combustion, metal chemistry, and the careful design of materials to produce light, color, sound, and movement. Understanding the chemical reactions at play in fireworks helps us appreciate their beauty and complexity. While fireworks are a source of celebration and wonder, they also highlight the importance of balancing chemistry with safety and environmental awareness.