Air and Combustion

1. Nitrogen (78%) – the most abundant gas
2. Oxygen (21%) – essential for breathing and combustion
3. Carbon dioxide (0.03%) – used by plants in photosynthesis
4. Noble gases (about 1%) – such as helium, neon, argon
5. Water vapor – varies in amount depending on the weather

Combustion is a chemical process where a substance reacts rapidly with oxygen to produce heat and light. It is also known as burning.

Examples of substances that can undergo combustion:

• Paper
• Dry grass
• Charcoal
• Kerosene
• Wood

Note: Combustion is a chemical change because new substances are formed, and the change is usually irreversible.

1. Water vapor
2. Carbon dioxide
3. Smoke or soot (depending on the substance and how complete the combustion is)

Combustion is used in many ways in our daily lives. Below are some of its important applications:

1. Generation of energy Human beings use combustion to produce fuel energy for cooking, lighting, and running machines.
2. Transport Most vehicles such as cars, buses, and motorcycles run on fuels like petrol or diesel. These fuels undergo combustion in the engine to produce energy that powers the vehicle.
3. Extraction of metals Large amounts of air (oxygen) are used in the combustion process to extract metals like:

• Zinc
• Iron
• Copper
• Gold

These metals are then used to make machines, coins, water pipes, electric cables, and other household items.

4. Welding and cutting metals A mixture of ethyne (acetylene) and oxygen gas is burned to produce a very hot flame (up to 3000°C). This flame is used to:

• Melt metals
• Cut through hard metal surfaces
• Join metals together during welding