Chapter - 6, Combustion and Flame, Science, Class 8

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Chapter - 6, Combustion and Flame, Science, Class 8

INTRODUCTION
COMBUSTION AND TYPES
IGNITION TEMPERATURE
INFLAMMABLE SUBSTANCE
SOURCES OF SOLAR ENERGY
TYPES OF COMBUSTION
FIRE EXTINGUISHER
FLAME
FUEL AND ITS TYPES
FUEL EFFICIENCY
GLOBAL WARMING
ACID RAIN

Every topic of this chapter is well written concisely and visuals will help you in understanding and imagining the practicality of all the topics.

By Shivam Parmar (Entrepreneur)

1. CHAPTER –6
COMBUSTION AND FLAME
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2. INTRODUCTION
•We use different kinds
of fuel for various
purposes at home, in
industry and for running
automobiles.
•The materials which
produce heat energy on
burning in air are called
fuels.

3. COMBUSTION AND
ITS TYPES
What is combustion ?
•The process ofproduction of
heat and light by the burning
of a combustible substance
in the presence of air is
called combustion. e.g.
magnesium burn to form
magnesium oxide and
produces a dazzling white
flame and a large amount of
heat energy.

4. Substance
Combustible
E.g. wood, paper,
magnesium,
Kerosene oil,
charcoal etc.
Non-Combustible
E.g. Iron nails,
Stone piece, Glass
etc.

5. IGNITION TEMPERATURE /
KINDLING TEMPERATURE
“The lowest temperature at
which a substance catches fire is
called its ignition temperature”.
E.g. Ignition temperature of
phosphorous is 35
o
C. So unless
the phosphorous is heated to
35
o
C, it will not catch fire.
However if temperature of air is
35
o
C or more, phosphorous will
catch fire without heating.

6. INFLAMMABLE SUBSTANCES
•The substances which have very
low ignition temperature and can
easily catch fire witha flame are
called inflammable substance.e.g.
Petrol, alcohol, LPG etc., have low
ignition temperatures.
•Ignition temperature of
inflammable substances is
generally less than 100
o
C. Excess
supply of supporter of
combustion leads to complete
combustion.

7. CONDITIONS NECESSARY FOR COMBUSTION
There must be a combustible
substance.
There must be a continues supply of
oxygen or air.
The temperature of combustible
material should be above its ignition
temperature.

8. SOURCE OF
SOLAR ENERGY
•Sun neither use conventional
combustible materials nor
does it use oxygen or air as
supported combustion.
•The 98% mass of sun is made
of hydrogen which is at very
high temperature.
•At this high temperature
hydrogen atoms fused in one
another to form helium
atoms.

9. TYPES OF
COMBUSTION
There are four types of
combustion
a)Slow combustion
b)Rapid Combustion
c)Spontaneous
Combustion
d)Explosive Combustion

10. SLOW COMBUSTION
•When a combustible material
burns at a slow or moderate
rate, it is called slow
combustion.
•During slow combustion there
is not sufficient supply of air,
thus, combustion is never
complete and as a result more
or harmful gases are formed.
e.g. cow-dung cakes, wood,
kerosene oil lamp.

11. RAPID
COMBUSTION
•When a combustible material
(generally gas) burns rapidly to
produce heat and light, it is called rapid
combustion. e.g. LPG and CNG,
magnesium ribbon, match stick, dry
grass etc.
•During rapid combustion, there is
sufficient supply of air and hence the
combustion is complete.

12. SPONTANEOUS
COMBUSTION
•The combustion in which a material
suddenly bursts into flames, without
the application of any apparent cause
is called spontaneous combustion or
combustion that occurs without the aid
of any external heat is known as
spontaneous combustion.
•When a small piece of phosphorous or
sodium is kept in air for some time, it
suddenly burst into flames.

13. •These materials initially form
their oxides and produce heat
energy which increases the
temperature above ignition
temperature and they
suddenly burst into flame.
•Forest fires are also the result
of spontaneous combustion
because there is a combustible
material, a supporter of
combustion and the right
ignition temperature.

14. EXPLOSIVE
COMBUSTION
•When a mixture of combustible
material and air completely burns in a
very short span of time in same closed
space, explosion combustion takes
place.
•When a sudden reaction takes place
with the evolution of heat, light and a
large amount of gas formed in the
reaction is liberated is called
explosion.
•Examples: Bursting of crackers, shot of
a gun etc.

15. •Explosion can also take
place if pressure is
applied on the cracker.
•During explosive
combustion, generally
there is internal supply of
oxygen or air.

16. FIRE EXTINGUISHER
•The job of fire extinguishers
is to cut off the supply of air
to bring down the
temperature of the fuel or
both.
•One of the most common
fire extinguisher is Soda Acid.
•Water is the most common
fire extinguisher for wood or
paper.

17. •Combustion of most fuels releases
carbon dioxide in theenvironment.
Increased concentration of carbon
dioxide in the air isbelieved to
cause Global Warming. It happens
due to rise intemperature of the
atmosphere of the earth, melting
of polarglaciers, which leads to
rise in the sea level causing floods
in thecoastal area.
•Burning of coal and diesel releases
Sulphur dioxide gas. It is an
extremely suffocating and
corrosive gas.

18. •Petrol engines give off gaseous
oxides of nitrogen.
•Oxides of Sulphur and nitrogen
dissolve in rain water and from
acids. Such rain is called Acid
Rain. It is very harmful for
crops, buildings and soil.
•Now use of diesel and petrol is
replaced by Compressed
Natural Gas (CNG) because it
produces the harmful product
in very small amount and is a
cleanser fuel.

19. FLAMES
•A region of burning gases is
called flame.
•A flame is a zone where the
burning of gases or vapour
takes place with the
production of light and
heat. A flame results due to
rapid combustions of fuel.

20. FUELS AND THEIR TYPES
“Any substance which is
easily available cheaper
and burns in air at a
moderate rate, producing
a large amount of heat
energy, without leaving
behind any undesirable
residue is called a fuel”.

21. FUEL
EFFICIENCY
•Different types of fuels have
different efficiency, which is
measured in their calorific
value.
•Fuel may be categorized on
the basis of their individual
calorific value.

23. GLOBAL
WARMING
•The CO
2in air traps the heat
of the sun radiated back by
the earth.This makes the
air warm and comfortable
for living beings and in-fact
makes it possible for life on
earth to exist.

24. EFFECT OF
GLOBAL
WARMING
•Scientists believe that
the average global
temperature may rise
as much as 2
o
C by the
end of the century.
•This can cause large
scale melting of ice in
the polar regions and
also expansion of
ocean water.

25. ACID RAIN
•Sulphur is present in coal as
an impurity. When coal is
burnt in homes, factories or
power plants Sulphur dioxide
is given off. Sulphur dioxide is
poisonous, it affects our
lungs.
•It combines with the oxygen
in the air to form Sulphur
trioxide (SO
3). This reacts with
water in the clouds to form
Sulphuric acid (H
2SO
4).

26. EFFECT OF
ACID RAIN
•The water of lakes and
rivers becomes acidic and
thus unsuitable for
aquatic plants and
animals.
•The soil becomes acidic
and therefore unsuitable
for cultivation.
•Sculptures, monuments
and buildings are eroded.

27. Thank You
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and other PPTs. Email me for more PPTs
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