Coal, Petroleum and Combustion: Class 8 Study Guide
Fossil fuels formed from ancient living things. Burning them releases energy and gases.
Coal formed over millions of years from dead plants buried under pressure and heat. Petroleum and natural gas formed from tiny sea organisms. These are fossil fuels. They are non-renewable, so we must use them carefully.
Petroleum is refined by fractional distillation into useful parts.
Products of fossil fuels
| Fossil fuel | Products | Uses |
|---|---|---|
| Coal | Coke, coal tar, coal gas | Steel, power stations, chemicals |
| Petroleum | Petrol, diesel, kerosene, LPG, paraffin wax, lubricating oil | Vehicles, cooking, lighting, machines |
| Natural gas | CNG, a cleaner fuel | Vehicles, cooking, fertiliser |
Combustion
Combustion is burning in oxygen to give heat and light. It needs three things: fuel, air (oxygen) and heat to reach the ignition temperature. A flame has three zones: the dark inner zone (unburnt gas), the bright middle zone (partly burnt) and the outermost zone, which is the hottest because burning is complete there. A good fuel has a high calorific value, the heat given out per kilogram.
Something that burns.
From the air.
To reach ignition temperature.
The fire goes out.
Putting out fires
Water cools burning wood and paper. For fires in oil or electrical equipment, never use water. Use a carbon dioxide extinguisher, which cuts off the air, or smother the flames with a thick cover. Call the fire brigade and get out safely.
Worked examples and common mistakes
Example: Which zone of a flame is hottest? The outermost zone. Example: Why does a candle go out under a glass? Its oxygen is used up. Common mistakes: using water on an oil or electrical fire, and thinking that coal and petroleum are renewable. Burning fossil fuels adds carbon dioxide to the air and speeds up global warming.
Check your understanding: model answers
1. For example petrol and diesel. 2. A carbon dioxide extinguisher. 3. They took millions of years to form and are used faster than they form.
✨ Key Takeaways
- Fossil fuels formed from ancient living things.
- Combustion needs fuel, oxygen and heat.
- The outermost zone of a flame is the hottest.
- Never use water on oil or electrical fires.
💬 Questions for Discussion & Reflection
- Name two products of petroleum.
- Which extinguisher suits an electrical fire?
- Why are fossil fuels non-renewable?
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