In the sun, heat and
light are produced
by nuclear reactions.
The lowest temperature at which a
substance catches fire is called it’s
Ignition temperature of
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
The substances which have very low
ignition temperature and can easily
catch fire with a flame are called
c) LPG( Liquified Petroleum Gas)
How can fire be extinguished?
Fire can be extinguished by:-
a) Removing the combustible substance
b) Cutting off the supply of Oxygen.
c) Reducing the temperature of the fuel
below its ignition temperature.
Water is an excellent extinguisher when
it comes to paper, wood.
Water cools the combustible substance
below the ignition temperature so that
the combustion is stopped.
Water vapors also surround the flame
so the supply of Oxygen is cut off.
Fireman extinguishing fire using water as extinguisher
Fire Extinguisher Co
Carbon dioxide is also a very effective extinguisher in
all the cases especially involving electrical appliances
and oil as in such cases water cannot be used.
Types of Combustion
Combustion can be classified into
a) Rapid Combustion
b) Spontaneous Combustion
d) Slow Combustion
The combustion in which a substance burns
rapidly and produces heat and light is called
a) Burning of white Phosphorus at room
The type of
combustion in which
a material suddenly
bursts into flames,
application of any
apparent cause is
Examples of Spontaneous
Forest Fires caused by
Spontaneous combustion of coal
dust in coal mines.
A sudden reaction that takes place with
the evolution of heat, light and sound. A
large amount of gas is formed in the
reaction is liberated. Such a reaction is
called an ‘Explosion.’
a) Burning of crackers
The type of combustion which takes place at a
slow rate at low temperatures is called ‘Slow
b) Rusting of Iron.
A flame is the visible, gaseous part of a fire. It
is caused by a
highly exothermic reaction taking place in a
thin zone. Some flames are hot enough to
have ionized gaseous components of sufficient
density to be considered plasma. However, a
candle flame which has a temperature below
1500 °C produces too low an ion density to be
considered a plasma.
Substances which give out flame.
The substances which vaporize during
combustion give flames.
a) Kerosene and Wax burn with a flame
b)Whereas Charcoal, on the other hand, does
not vaporize and so does not produce a
zone of a flame
with a metallic
melting gold and
The amount of heat energy
produced on complete
combustion of 1kg of a fuel is
called its ‘Calorific Value’
The calorific value of a fuel is
expressed in a unit called
‘Kilojoule per kg (kJ/kg)
Calorific Value of different Fuels
Fuel Calorific Value (kJ/kg)
Cow dung cake 6000-8000
Disadvantages of burning fuels
Carbon fuels like wood, coal, petroleum
release unburnt carbon particles. These
are pollutants and cause respiratory
Incomplete combustion of these fuels
gives Carbon Monoxide gas. It is a very
poisonous gas and can kill people who
inhale this gas.
Disadvantages of burning fuels
Combustion of most fuels releases
carbon dioxide in the environment.
Increased concentration of this gas
leads to ‘Global Warming’.
Burning of coal and diesel releases
oxides of Sulphur and nitrogen dissolve
in rain water and form acids. Such rains
are called ‘Acid Rains.’
Global Warming is the rise in
temperature of the atmosphere of the
earth. This results in the melting of
polar glaciers, which leads to rise of the
water in the sea. Low lying coastal areas
may even be submerged under water.