IT IS A PPT ON A CHAPTER OF SCIENCE..IT WILL HELP IN EASY GRASPING OF THE CHAPTER..

2. What is Combustion ?
•Combustion – The chemical process in which a substance burns in air, or oxygen ,
with the release of heat and light energy is called combustion.

3. What are the combustible materials ?
•Combustible material – The materials which on heating in the presence of air or
oxygen, catch fire easily and produce heat and light energy,
are called combustible materials.
Burning of wood Burning of petrol
(fossil fuel)

4. What are combustible substances or fuel ?
• Combustible substances or fuel – The substance that undergoes combustion is
called a combustible substances or fuel. A
fuel may be solid , liquid or gas.
Coal (Solid) Petrol
(Liquid)
Natural Gas
(Gas)

5. What is the supporter of combustion ?
• Oxygen, present in air, helps in the combustion of a fuel. It is therefore,
called a supporter of combustion.

6. What is kindling temperature or ignition temperature ?
• The ignition temperature or kindling temperature is the lowest temperature at which a
combustible substance catches fire.

7. What are the conditions for combustion ?
The conditions are –
➢There must be a combustible substance.
➢There must be a continuous supply of oxygen in air.
➢The temperature should be above the ignition temperature of the combustible
material.

8. Types of combustion
1. Slow Combustion
2. Rapid Combustion
3. Spontaneous Combustion
4. Explosive Combustion

9. Slow Combustion
➢When a combustible material burns at a slow, or moderate rate, its combustion is
called slow combustion.
➢Slow combustion usually occurs when there is insufficient supply of air.
➢Such a combustion never gets really completed.
➢Burning of cowdung cakes,woods, burning of piece of paper etc are some
examples of slow combustion.

10. Rapid Combustion
➢When a combustible substance burn at a fast rate , its combustion is called
rapid
combustion.
➢Rapid combustion occurs when there is a sufficient supply of air.
➢The combustion in such cases is completed.
➢For example a candle.

11. Spontaneous Combustion
➢When a combustible substance catches fire on its own, even at room temperature,
its combustion is referred to as spontaneous combustion.
➢A piece of sodium metal or phosphorous are observed to undergo spontaneous
combustion when kept in air.
➢For example forest fires.

12. Explosive Combustion
➢When a mixture of combustible material and air burns completely, in a very short span of time in a
closed space, an explosive combustion can take place.
➢The combustible material, in such cases, burns uncontrollably in free supply of air and releases a
very large amount of heat. This often produces the sound of an ‘explosion’.
➢For example when a cracker is ignited, a sudden and rapid reaction takes place.
➢A reaction accompanied by (an explosive) sound, is called explosion.

13. What happens when incomplete combustion takes place ?
•A part of this unburnt carbon passes into the atmosphere in the form of soot.This only wastes the fuel
but also pollutes the atmosphere.
•Carbon monoxide is formed. This gas is highly poisonous and causes respiratory problems; it may also
prove to be fatal.

14. What is Flame ?
Flame may be defined as the region over which gases burn. When you burn a piece of paper, or wax
candle, a flame is produced.

15. Layers of Candle
➢Innermost zone
➢Middle zone or Luminous zone
➢Outermost zone or Non luminous zone

16. Innermost Zone and Middle Zone
•Innermost zone
➢This zone consists of unburnt wax vapour given off by the
molten wax.
➢It is coldest part of the flame.
•Middle zone or Luminous zone
➢In this zone, partial combustion of wax vapours takes place
with the liberation of a lot of energy.
➢This energy partly decomposes the wax vapour into carbon
particles.
➢This zone of the flame is hotter than the dark inner zone; it is
yellow in colour

17. Outermost Zone or Non-Luminous Zone
➢It is a zone of complete combustion of wax vapours
and carbon particles.
➢The air, from the sides of the flame, mixes with unburnt
wax vapours and carbon particles and burns them
completely to form carbon dioxide gas and water vapours.
➢It is the hottest part of the flame.

18. Fuel and Calorific Value
➢The amount of heat energy produced on completely burning one kilogram of a fuel in pure oxygen
is called the calorific value of a fuel.
➢A fuel produces more heat energy per kilogram is said to have higher calorific value.
➢The more the calorific value, the better is the efficiency of a fuel.
➢Calorific value is expressed in kilojoules per kilogram (KJ/KG)

19. Calorific Value of different fuels

20. Characteristics of a Good fuel
A good fuel should –
•be cheap, readily available and easy to
transport.
•be easy to store
•have a high calorific value.
•not produce harmful gases after burning.
•have a low ignition temperature;
however, this should not be below, or
around the room temperature.
•undergo complete and controllable
combustion

21. Harmful Effects of Fuels
1. Fuels, like wood, coal and petroleum products, release unburnt carbon
particles. These carbon particles of smoke , or ash, get suspended in the air.
Excessive amount of these particles in the air causes breathing problems. In
winter, these particles produce ‘smog’ which is very harmful to plants as well
as animals.
2. Incomplete combustion of carbon fuels results in the formation of carbon
monoxide gas. It is a very poisonous gas. Even small amounts of it can prove
fatal.

22. EXCERCISES
➢Fill in the blanks
1. Calorific value is expressed in _____ per ______.
2. The materials which on heating in the presence of ______ or oxygen, catch
fire easily and produce _______ and ________energy are called ________
materials.
3. The _______ process in which a substance burns in _______ or oxygen,
with the release of heat and _________ energy is called _________.
4. The ______temperature, at which a (combustible) substance catches fire, is
called its _______.
5. The carbon dioxide in our ________, acts as a fire _________.

23. ➢True or False
1. When you burn a piece of paper, or a wax candle, oxygen is produced. ____________
2. Middle zone of the flame is yellow in colour. ____________
3. Rapid combustion occurs when there is a sufficient supply of air. ____________
4. Wax vapours are present in the outermost zone of the candle flame. ____________
5. Combustion of (most)fuels releases carbon dioxide in the environment. ____________

24. ➢Match the following
(A) (B)
1. Petrol 210 degree celsius
2. Coal 425 degree celsius
3. Methane 560 degree celsius
4. Hydrogen 500 degree celsius
5. Ethylene 454 degree celsius
6. Diesel 246 degree celsius

25. ➢Crossword Puzzle
▪ Down
1.When a combustible material burns at a slow, or moderate rate, its combustion is
called.
5.A reaction accompanied by (an explosive )sound is called what ?
7.Which is better domestic fuel ?
10.Who is called the supporter of combustion?
▪ Across
2. When a combustible substance catches fire n its own, even at room temperature, its combustion is referred to as
what type of combustion ?
3.What is the fuel for our body ?
4.Which is the hottest part in the flame of a candle ?
6.A good fuel should be what ?
8.A good fuel should be easy to what ?
9.Which gas produces less harmful products ?

26. Crosword Puzzle
S e
B
S
C
F
I
C
2
1 5
4
8
9
7
3
6

27. ➢Answers
★ Fill in the blanks
1. kilojoules, kilogram
2. air, oxygen, heat, light, combustion
3. chemical, air, light, combustion
4. lowest, ignition
5. breath, extinguisher

28. ➢TRUE / FALSE
1. False
2. True
3. True
4. False
5. True

29. ➢Match the Following
1. 246 degree celsius
2. 454 degree celsius
3. 500 degree celsius
4. 560 degree celsius
5. 425 degree celsius
6. 210 degree celsius

30. ➢Crossword Puzzle
DOWN
1.Slow
5. Explosion
7. LPG
10. Oxygen
ACROSS
1. Spontaneous
3. Food
4. Blue
6. Cheap
8. Store
9. CNG