1. COMBUSTION AND FLAME: HOW TO SAVE
ENERGY IN ITS
COMBUSTION AND FLAME
INTRODUCTION
A chemical process in which a substance reacts with oxygen to give off heat terms
as combustion. In combustion and flame we come to know that the substance that undergoes
combustion is we know as combustible. It is also called fuel which can be solid, liquid or gas. During
combustion, sometimes light evolves as a flame e.g. when coal, wood, magnesium are burnt these produce
heat and light.
NECESSARY CONDITIONS FOR COMBUSTION IN
COMBUSTION AND FLAME
 Occurrence of a combustible substance.
 Presence of a supporter of combustion.
 Heating of a combustible substance to its ignition temperature or attainment of ignition
temperature.
COMPARATIVE STUDY OF VARIOUS
SUBSTANCES
COMBUSTIBLE
SUBSTANCE
NON-COMBUSTIBLE
SUBSTANCE
INFLAMMABLE
SUBSTANCE
The substances which burns in
air or oxygen
This does not burn in air or
oxygen
The substance which has very
low ignition temperature and
can catch fire easily with a
flame
e.g. petrol, paper, kerosene e.g. water, glass, sand e.g. petrol, alcohol, LPG
SUPPORTER OF COMBUSTION:
A substance which helps in combustion is called a supporter of combustion e.g. oxygen, air etc.
IGNITION TEMPERATURE:
Before a substance catches fire and starts burn, we must heat the substance to a certain minimum
temperature by supplying heat. The lowest temperature at which a substance catches fire and starts burning
terms as ignition temperature. A combustible substance cannot catch fire if its temperature is lower than its
ignition temperature.
HOW DO WE CONTROL FIRE IN COMBUSTION AND
FLAME
COMBUSTION AND FLAME: We have learnt that there are three essential requirements for producing fire.
If anyone can remove any of these three things then the burning procedure will stop and fire extinguishes.
Thus Fire extinguishing procedure are of three types:
 By removing the fuel, but in most cases, fuel cannot be eliminated.

2.  if we remove the heat.
 By cutting off the air supply to the burning substances.
TYPES OF FIRE EXTINGUISHER:
 WATER: It is the most common fire extinguisher. But we can be use it only in fire on paper and wood.
Water extinguishes fire by cooling the burning substances.
 CARBON DIOXIDE (in liquid form) : It extinguishes fire arising from electrical equipment and
inflammable substances like petrol, kerosene etc. CO2 is denser than air and thus forms a layer around
the burning substance. This gas covers the fire like a blanket so that fresh air cannot reach the burning
substance.
 CARBON DI OXIDE ( in the form of dry powder of baking soda and potassium
bicarbonate) When we release this powder through extinguisher machine , it reduces the heat
released by the fire.
TYPES OF COMBUSTION
There are various types of combustion. three important types of combustion are:
 RAPID COMBUSTION : In this combustion in short time large amount of heat and light evolve , like
burning of cooking gas (LPG) in a gas stove.
 SPONTANEOUS COMBUSTION: It occurs on its own without the help of any external heat, like
burning of white phosphorus in air at room temperature.
 EXPLOSIONS: It is a sudden combustion resulting formation of a large amount of heat, light and sound
are ,like bursting of cracker.
PROBLEMS RELATED TO COMBUSTION AND FLAME:
Qs1 As a result of incomplete combustion which harmful gas evolves?
Ans1 Carbon monoxide which is a poisonous and harmful gas evolves as a result of incomplete
combustion.
Qs2 Why is the use of diesel and petrol as fuels in automobiles being replaced by Compressed natural Gas
(CNG) in big cities?
Ans2 It is because CNG produces harmful pollutants in very small amount, so, it
is a clean fuel.
ANSWER IN BRIEF ON COMBUSTION AND FLAME)
Qs3 How heat is produced in our body?
Ans3 In our body, food is broken down by reavtion with oxygen. During such reactions, heat is
produced, this heat keeps our body warm.
Qs4 Name two fuels which we use in our homes for cooking food?
Ans4 Two fuels which we use in our homes for cooking food are LPG and kerosene oil.
GIVE REASONS ON COMBUSTION AND FLAME
Qs5 Which type of fuel produces flame? Does charcoal burn with flame?
Ans5 The substances which vaporise during burning produce flame.
No, charcoal does not burn with flame, it glows only because it does not vaporise on burning.
Qs6 Do all substances catch fire at the same temperature?

3. Ans6 No, all the substances do not catch fire at the same temperature. Different substances need
different temperature to catch fire which is called ignition temperature.
HIGHER ORDER THINKING SKILL
Qs7Like fuels, the sun also provides heat and light. What is the source of heat and light in the sun?
Ans7 In the sun, nuclear reaction takes to produce heat and light .
SHORT TYPE QUESTION
Qs8 When combustion takes place what are the products?
Ans8 The products of combustion are carbon dioxide, water vapour, heat and light.
Qs9 Why do we cover a with a blanket when the clothes of that person catch fire?
Ans9 When the clothes of a person catch fire, we must cover the
person with a blanket for extinguishing the fire. This is because the
supply of air to the burning clothes cut off by blanket. Due to which
the clothes stop burning and fire gets extinguished.
EXPLAIN THE FOLLOWING ON COMBUSTION AND FLAME
Qs10:We know that wood contains large amount of calorific value, we still discourage its use as a fuel.
Explain.
Ans10: Burning of wood has several disadvantages in combustion and flame. These are as follows:
 By burning wood huge amount of smoke is produced which causes respiratory diseases.
 We use to cut down trees to get wood which we use as fuel. This activity leads to deforestation
which is very harmful to the environment.
 Trees provide us many useful substances. But deforestation reduces our naturel resource like
wood.
Qs11: A girl Manu heated oil for frying aloo chips. Suddenly oil catches fire, she poured water to
extinguish the fire. Do you think, this action was suitable? If yes, why? If not, why not? What should be her
duty in thius dangerous condition?
Ans11: If she pours water to extinguish fire it will be worst condition. It is because oil is lighter than
water. So, water will settle down below the oil. In this case Manu should use sand or soil. That sand
or soil can cut off the air supply to the fire. Thus, fire can be controlled. But sometime we cannot get
sand or soil easily.
So, Manu must switch off the burner and put a lid on the frying pan. When Manu will do this activity,
the contact between fuel and oxygen is disconnected, followed by putting off of flame.