NCERT Revision Notes Chapter 6 Combustion and Flame Class 8 Science

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• Introduction

• Combustion

• Ignition temperature

→ Inflammable substances

• Supporter of combustion

• Control of fire

• Types of combustion

→ Rapid combustion

→ Spontaneous combustion

→ Explosion

• Zones of candle flame

• Fuel efficiency

• Calorific value

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→ Fuels are used to get energy in the form of heat. Cowdung, wood, coal, charcoal, petrol, diesel, compressed natural gas (CNG), etc. are the examples of fuels.

→ Candle burns with a flame whereas coal does not.

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→ It is a chemical process in which a substance reacts with oxygen to give off heat and light.

→ Oxygen (in air) is essential for combustion.

→ Substances that burn in air are called combustible substances (also called fuels) and those that do not burn in air are non-combustible substances.

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Ignition temperature:  It is the lowest temperature at which a substance catches fire.

Inflammable substances: They have very low ignition temperature and can easily catch fire with flame.

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→ The gaseous environment that supports combustion of a combustible substance is called supporter of combustion.\

→ Smaller the size of combustible particles, faster is the rate of combustion.

→ Nature of combustible substances: Inflammable substances burn faster as compared to substances such as wood.

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→ Water is commonly used to extinguish fire. It is not suitable for fires involving oil, petrol, and electrical equipments.

→ For fires involving oil, petrol, and electrical equipments, carbon dioxide is the best extinguisher.

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→ Dark zone (middle zone), luminous zone (innermost zone), and non-luminous zone (outer zone).

→ A good fuel is one which is cheap is readily available burns easily in air at a moderate rate produces large amount of heat does not leave behind any undesirable substances.

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Fuel efficiency

→ It is expressed in terms of calorific value. The unit is kilo joule per kg.

Calorific value

→ It is the amount of heat energy produced by complete combustion of 1 kg of a fuel.

→ It is expressed in Kilo joule per kg (kJ/kg).