Combustion

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Slide1:

By, Sameer D. Devidas

Slide2:

What is combustion? A chemical process in which a substance reacts with oxygen to give out heat is called combustion. Example:- Burning of Magnesium ribbon.

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The substance that undergoes combustion is said to be combustible substances. It is also called a fuel. Fuels exist in three states:- Solid Liquid & Gaseous

Solid Fuels:

Solid Fuels Charcoal Wood Cow dung cakes coal

Liquid Fuels:

Liquid Fuels kerosene diesel petrol ethanol

Gaseous fuels:

Gaseous fuels LPG CNG Bio gas Coal Gas

Conditions Necessary for Combustion:

Conditions Necessary for Combustion Combustion takes place only if there is: Fuel Air ( To supply oxygen) Heat ( To raise the temperature beyond ignition temperature)

Ignition Temperature:

Ignition Temperature A substance has to heated to a certain minimum temperature before it can catch a fire. The minimum temperature at which a substance catches fire and burns is called its ignition temperature.

Ignition Temperature:

Ignition Temperature A substance will not catch fire and burn if its temperature is lower than its ignition temperature. Substances which have very low ignition temperature and can easily catch fire with a flame are called inflammable substances. Eg :- petrol, alcohol, LPG, CNG etc.

Ignition temperature of different materials:

Ignition temperature of different materials Material Ignition Temperature White Phosphorus 35 degree Celsius Petrol 246 degree Celsius Kerosene 220 degree Celsius Diesel 210 degree Celsius Wood 300 degree Celsius Coal 454 degree Celsius Piece of paper 233 degree Celsius

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TYPES OF COMBUSTION RAPID COMBUSTION SPONTANEOUS COMBUSTION EXPLOSIVE COMBUSTION

Rapid Combustion:

Rapid Combustion The combustion in which a substance burns rapidly and produces heat and light with the help of external heat is called ‘Rapid Combustion.’ Example:- The gas burns rapidly and produces heat and light when a burning match stick or a gas lighter is brought near a gas stove in the kitchen.

Spontaneous Combustion:

Spontaneous Combustion The type of combustion in which a material suddenly bursts into flames, without the application of any external heat is called Spontaneous Combustion. phosphorus burns spontaneously at room temperature

Examples of Spontaneous Combustion:

Examples of Spontaneous Combustion Forest Fires caused by heat of the sun or due to lightning strike Spontaneous combustion of coal dust in coal mines .

Explosion:

Explosion A combustion in which a substance burns suddenly with the evolution of heat, light and sound with the help of heat and pressure. Such a reaction is called an ‘Explosion.’ Example:- Burning of crackers

Slow Combustion:

Slow Combustion The type of combustion which takes place at a slow rate at low temperatures is called ‘Slow Combustion.’ Example:- Respiration Rusting of Iron.

HOW TO CONTROL FIRE?:

HOW TO CONTROL FIRE? . Remove the combustible material. . Reduce temperature to the ignition temperature of the combustible substance. . Cut off air supply.

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water Water is the most common fire extinguisher. It can be used only when materials like wood , paper etc. are on fire. Water cannot be used if electrical equipments are on fire because water conducts electricity and can harm those trying to put out the fire.

Carbon dioxide:

C arbon dioxide Carbon dioxide is the best fire extinguisher to put out fire caused by inflammable materials like oil and petrol and electrical equipments. Carbon dioxide is heavier than air and it covers the fire and cuts off the supply of oxygen and puts out the fire.

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Flame A flame is a visible gaseous part of a fire. It is caused by highly exothermic reaction taking place in a thin zone

Substances which give out flame:

Substances which give out flame The substances which vaporize during combustion give flames. Example:- Kerosene and Wax burn with a flame Whereas Charcoal, on the other hand, does not vaporize and so does not produce a flame.

Structure of a candle flame :-:

Structure of a candle flame :- A candle flame has three main zones. They are:- i ) Outer zone ii) Middle zone iii) Inner zone In the outer zone complete combustion of the fuel takes place and the colour of the flame is blue and is the hottest part of the flame. It is the non luminous part of the flame. In the middle zone partial combustion of the fuel takes place and the colour of the flame is yellow and is moderately hot part of the flame. It is the luminous part of the flame. In the inner zone there are unburnt vapours of the fuel and the colour is black and is least hot part.

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References Textbook: Science ahead standard 7 th Oxford New Science in Everyday Life https://en.wikipedia.org/wiki/Combustion http://www.innovateus.net/earth-matters/what-are-different-types-combustion-systems

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