The process of burning of substances in air
with the release of heat and light is called
A substance that Burns in air to produce heat
and light is called
Eg: Wood, Petrol
A substance that does not burn in air is called a
Eg: Stone, Metal
During combustion substances like coal or
charcoal react with oxygen in air to form
Carbon + Oxygen= Carbon dioxide + Heat
Hydrogen reacts with oxygen to form water.
Hydrogen + Oxygen = Water + Heat
Methane reacts with oxygen which burns to
produce carbon dioxide and water.
Methane + Oxygen = Carbon dioxide + Water +
Combustion takes place only if there is
A substance has to heated to a certain
minimum temperature before it can catch a fire.
This temperature is different in different
objects. In petroleum the ignition temperature
is very less.
The minimum temperature at which a
substance catches fire is called its ignition
Rapid combustion – occurs when a
substance burns rapidly to produce heat and
light. Ex- LPG , paper , wick of an oil lamp.
Spontaneous combustion – occurs when a
substance starts burning suddenly even
without being heated. Ex- white phosphorus
whose ignition temperature is 35°C
Explosion – is a combustion reaction that
occurs suddenly when a material is heated
liberating a large amount of heat , light and
An uncontrolled fire can be disastrous –
it can destroy life and property in
For the prevention of an uncontrolled
fire each city has fire stations equipped
with fire-fighting equipment . Water and
fire extinguishers are used to put out
. Remove the combustible material.
. Reduce temperature to the ignition
temperature of the combustible
. Cut off air supply.
Dry powder fire extinguisher – it contains
baking soda (NaHCO3).When this mixture is
thrown over a fire , baking soda decomposes
to release carbon di oxide which
extinguishes the fire.
Soda-acid fire extinguisher – it consists of a
small glass bottle filled with sulphuric acid
that is supported in a strong iron vessel
containing sodium bicarbonate. On striking
the knob, the bottle containing acid breaks
and carbon di oxide is liberated by the action
of the acid on baking soda.
Foam fire extinguisher – in this a
solution of aluminium is taken in the
glass bottle instead of sulphuric acid. It
releases a foam of carbon di oxide that
surround the burning substance and cuts
off its air supply. This type of fire
extinguisher is especially used to
extinguish oil fires.
Combustible materials such as wood,coal,gas or oil
which are burnt to produce heat or power are
known as fuels.
Solid fuels are easy to store but difficult to
Gaseous fuels are difficult to store; they have
to be compressed at high pressures and are
stored in sealed cylinders or tankers. These
can be dangerous if a leak develops because the
fuel can spread very fast. However gaseous
fuels are easy to use.
Liquid fuels can be stored easily and are easy
calorific value of fuel.
note: the higher the calorific value the better the
joule per kilogram
kilojoule per kilogram
It should have a high calorific value.
It ignition temperature should be neither too low nor
It should be cheap and readily available.
It should be easy and safe to transport, handle and
It should not cause air pollution upon burning.
It should not leave behind solid residue upon burning.
No fuel really meets all the characteristics listed
here. Natural gas is the closest to an ideal fuel.
Considerable research is being done to produce efficient
fuel cells that use hydrogen and oxygen to produce
Carbon monoxide and soot are also produced during the
combustion of other fuels. They are highly undesirable
byproducts of combustion. The fine particles of soot are called
suspended particulate matter (spm).They are dangerous
pollutants of air and can cause respiratory problems.
Some fuels like diesel & coal contain sulphur, which changes to
sulphur dioxide (SO2) upon combustion. Engines give out oxides
Both sulphur dioxide and the oxides of Nitrogen are
undesirable and harmful byproducts of combustion.
Besides being poisonous themselves, they dissolve in rainwater
to form acids and cause acid rain.
The carbon dioxide released during combustion
can result in an increased percentage of gas in
air. An atmosphere with excess carbon dioxide
traps more heat- this is called greenhouse
effect. Many scientists believe that this can
result in the average temperature of the
earth. This phenomenon is called global
warming. Global warming can lead to the
melting of polar ice causing flooding of low
lying costal lands and also cause climate
The process of burning of substances in air with the
evolution of heat and light is known as combustion.
A substance that burns in air to produce heat and
light is called a combustible substance. A substance
that does not burn in air is called a non-combustible.
The conditions that must be met for combustion are:
presence of a combustible substance, presence of
oxygen(air) and attainment of ignition temperature.
The minimum temperature at which a substance
catches fire is called it’s ignition temperature.
The three types of combustion are rapid combustion,
spontaneous combustion and explosion.
A fire can be extinguished by removing the
combustible substance, reducing the temperature to
below the ignition temperature or by cutting out
the air supply.
Fire extinguishers mainly use carbon dioxide to
The important criteria for the selection of a fuel are
physical state, calorific value, ignition temperature,
combustion residue, emissions and cost.
The candle flame has four zones dark zone,
luminous zone, non luminous zone and blue zone.
The luminous zone produces light due to the
glowing of carbon particles. The non-luminous zone
is the hottest.
Calorific value of a fuel an be defined as the amount
of heat liberated when one kilo-gram of the fuel is
completely burnt in an sufficient supply of oxygen.
Natural gas is the closest to an ideal fuel.
Some harmful substances given off during
combustion are suspended particulate matter (SPM),
carbon dioxide, carbon monoxide, sulphur dioxide
and oxides of nitrogen.
1.The chemical reaction in which a fuel is burned to release heat
energy is called __________ .
2.Wood, paper, kerosene and LPG are examples of ________ .
Ans. Combustible substances
3.The _________ temperature is the minimum temperature at
which a fuel can catch fire.
4.Combustion of wood can be classified as __________
5.A soda-acid type fire extinguisher gives out _________ to
extinguish a fire.
Ans. Carbon dioxide
6._________ extinguisher is used to extinguish a fire.
Ans. Foam fire
7.The zone that produces light in a candle flame is
called the _______ zone.
8.The amount of heat evolved, in kilojoules, when one
kilogram of fuel is burnt completely is called ________
value of the fuel.
9._________ is caused by sulphur dioxide and oxides of
Ans. Acid rain
10. ______ _______ can cause flooding of low lying
Ans. Global warming
11.A substance burnt to obtain heat energy is called a
12.A foam fire extinguisher gives out a foam of
Ans. Carbon dioxide
13.The glowing ________ particles in the luminous zone
of a candle flame make it look yellow.
Ans. Unburnt carbon particles.