Class- VIII
Sub- Science
Chapter- Combustion and Flame
Combustion
• A
chemical process in which a substance reacts with oxygen to give off heat is
called combustion.
• Combustion
is a process in which a substance react with oxygen to give off heat and light
(Not necessary for all condition).
• The
substance that undergoes combustion is called as combustible or fuel.
Ignition Temperature “The
lowest temperature at which substance catches fire”
• A
combustible substance cannot catch fire or burn until its temperature is lower
than its ignition temperature.
• Inflammable
Substance “The substance which have low ignition Temperature and can easily catch
fire with a flame” Ex:- LPG, Petrol,
Alcohol etc.
HOW CAN WE CONTROL FIRE
• The
most common fire extinguisher is water. But water works only when things like
wood, paper, clothes, etc.
• If
electrical equipment is on fire, water may conduct electricity and harm those
who is trying to control fire with the help of water.
• Water
is also not suitable for fires involving oil and petrol.
• Water
is heavier than oil, so it sinks below the oil and oil keeps burning on the
top.
• To
control fires involving electrical equipment and inflammable materials (petrol,
oil) carbon dioxide (CO2) is the best extinguisher.
• CO2
is heavier than oxygen, it covers the fire like a blanket, since the contact
between the fuel and oxygen is cut off, the fire gets controlled.
• Also,
CO2 mostly does not harm electrical
equipment.
Note:-
CO2 is carbon dioxide due to error it is not arranged properly.
Types of Combustion
There are two types of combustion
1)Rapid Combustion
2)
Spontaneous Combustion
• The
gas burns rapidly and produces heat and light, such combustion is called as
Rapid Combustion.
• A
combustion in which a material suddenly bursts into flames, without the
application of any apparent ( means catch fire themselves due to natural
heating) cause is called Spontaneous Combustion.
Flames
• A
flame is the visible gaseous part of a fire.
• An
area of bright burning gas that comes from something that is on fire.
• Fire is a rapid oxidation of material.
Structure of Flames
A candle flame is consist of three zones
1)
Outer zone (Non luminous Zone)
2) Middle Zone (Luminous Zone)
3) Inner Most Zone / Dark
Zone (Least combustion)
Fuel
• Fuels
are those substances which produce heat and light energy on burning. Ex- wood,
petrol, coal, LPG etc.
• Ideal Fuel:-
Ideal fuel is basically cheap combustible and it produces a high among
of heat energy. Ex- Natural Gas, LPG
Fuel Efficiency
• The
amount of energy released per unit mass of the fuel is called fuel efficiency.
• The
amount of heat energy produced on complete combustion of 1kg fuel is called
calorific value.
• The
Calorific Value of a fuel is expressed in a unit is called Kilojoule per KG
(KJ/KG).
|
FUEL
Cow dung cake
Wood
Coal
Petrol
Kerosene LPG Hydrogen
|
KJ/KG (Calorific Value)
6000 – 8000
17000 – 22000
25000 – 33000
45000
45000
55000 150000
|
Harmful Effects on Environment of fuel
consumption
• Burning
of coal and diesel releases Sulphur Dioxide gas, which is one of the reason of
Acid rain.
• Most
of fuel combustion releases Carbon Dioxide, which causes of Global Warming.
• Incomplete
combustion of these fuels gives Carbon Monoxide gas. It is a very poisonous
gas.
Thanks for reading this post.
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