Kidz Olympiad🎉

Science Class 8 - Combustion And-Flame Notes

Comprehensive study notes for Class 8 - Combustion And-Flame olympiad preparation

Combustion and Flame

Welcome to the chapter on Combustion and Flame for Class 8. In this chapter, you will learn what combustion is, how flames are produced, the types of flames, and the conditions needed for burning. By the end of this chapter, you will understand the science behind burning and how to use fuels safely!

Introduction

Combustion is a chemical process in which a substance reacts with oxygen to give off heat and light. The visible part of burning is called a flame. We use combustion every day, from cooking food to running vehicles.

What is Combustion?

Combustion is the process of burning. It happens when a fuel reacts with oxygen and releases energy in the form of heat and light.

  • Example: Burning wood, coal, LPG, petrol.
  • Combustion needs three things: fuel, oxygen, and heat.

Types of Combustion

  • Rapid Combustion: Happens quickly and produces heat and light (e.g., burning of LPG).
  • Spontaneous Combustion: Happens on its own without an external heat source (e.g., burning of phosphorus).
  • Explosion: Combustion with sudden release of gases and energy (e.g., firecrackers).

What is a Flame?

A flame is the visible, glowing part of a fire. Not all substances produce a flame when they burn. Substances like kerosene and wax produce flames, while charcoal does not.

Structure of a Flame

  • Outer Zone: Hottest part, complete combustion.
  • Middle Zone: Moderate temperature, partial combustion.
  • Inner Zone: Coolest part, unburnt fuel.

Fuels and Their Efficiency

Fuels are substances that burn to give heat and energy. Good fuels burn easily, give lots of heat, and do not produce harmful smoke.

  • Examples: Wood, coal, petrol, diesel, LPG, CNG.
  • Calorific value: Amount of heat produced by burning 1 gram of fuel.

Conditions Needed for Combustion

  • Presence of fuel
  • Supply of oxygen (air)
  • Heat to start the reaction (ignition temperature)

How to Control Fire

  • Remove fuel
  • Cut off air supply (using sand, blanket, or foam)
  • Lower the temperature below ignition point (using water)

Harmful Effects of Burning

  • Air pollution (smoke, harmful gases)
  • Global warming
  • Health problems (breathing issues)

Fun Activity: Candle Flame Observation

Light a candle and observe the different zones of the flame. Try placing a metal object in each zone and see which part gets hottest!

Summary

  • Combustion is burning with heat and light.
  • Flames have different zones with different temperatures.
  • Fuels are used for energy; good fuels are efficient and clean.
  • Fire can be controlled by removing fuel, air, or heat.

Practice Questions

  1. What is combustion?
  2. Name three things needed for combustion.
  3. What is the hottest part of a flame called?
  4. Give two examples of fuels.
  5. How can you control fire?

Challenge Yourself

  • Draw and label the zones of a candle flame.
  • List three harmful effects of burning fuels.

Did You Know?

  • The blue part of the flame is the hottest!
  • CNG and LPG are clean fuels used in vehicles and homes.

Glossary

  • Combustion: Burning of a substance with heat and light.
  • Fuel: Material that burns to give energy.
  • Ignition Temperature: Minimum temperature needed to start burning.
  • Calorific Value: Amount of heat produced by burning 1 gram of fuel.

Answers to Practice Questions

  1. Combustion is the process of burning a substance to give heat and light.
  2. Fuel, oxygen (air), and heat (ignition temperature).
  3. Outer zone.
  4. Wood, coal, petrol, LPG (any two).
  5. By removing fuel, cutting off air supply, or lowering temperature.

Always be careful with fire and use fuels wisely to protect yourself and the environment!

Quick Navigation