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PPT - Combustion & Flame
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Page 1
CHAPTER - 6
COMBUSTION AND FLAME
Page 2
CHAPTER - 6
COMBUSTION AND FLAME
1) Combustible substances :-
Substances which burn in air to produce heat and
light are called combustible substances.
Eg :- wood, coal, charcoal, kerosene, petrol,
diesel, liquified petroleum gas (LPG), compressed
natural gas (CNG) etc.
Wood Coal LPG Kerosene
Page 3
CHAPTER - 6
COMBUSTION AND FLAME
1) Combustible substances :-
Substances which burn in air to produce heat and
light are called combustible substances.
Eg :- wood, coal, charcoal, kerosene, petrol,
diesel, liquified petroleum gas (LPG), compressed
natural gas (CNG) etc.
Wood Coal LPG Kerosene
2) Combustion :-
The chemical process in which a substance reacts with
oxygen to produce heat is called combustion.
The substance which undergoes combustion is called a
combustible substance. It is also called a fuel.
Sometimes light is also produced during combustion
either as a flame or as a glow.
Air is necessary for combustion.
Page 4
CHAPTER - 6
COMBUSTION AND FLAME
1) Combustible substances :-
Substances which burn in air to produce heat and
light are called combustible substances.
Eg :- wood, coal, charcoal, kerosene, petrol,
diesel, liquified petroleum gas (LPG), compressed
natural gas (CNG) etc.
Wood Coal LPG Kerosene
2) Combustion :-
The chemical process in which a substance reacts with
oxygen to produce heat is called combustion.
The substance which undergoes combustion is called a
combustible substance. It is also called a fuel.
Sometimes light is also produced during combustion
either as a flame or as a glow.
Air is necessary for combustion.
3) Air is necessary for burning :-
(a) (b) (c)
Fix a lighted candle on a table. Put a glass chimney over the table and rest
it on a few wooden blocks in such a way so that air can enter the chimney.
Observe what happens to the flame.
Now remove the blocks and let the chimney rest on the table. Again
observe the flame.
Then put a glass plate over the chimney. Observe the flame again.
The candle burns freely in (a) because air enters the chimney from below.
The candle stops burning in (b) because air does not enter the chimney
from below.
The candle does not burn in (c) because air is not available.
This shows that air is necessary for burning.
Page 5
CHAPTER - 6
COMBUSTION AND FLAME
1) Combustible substances :-
Substances which burn in air to produce heat and
light are called combustible substances.
Eg :- wood, coal, charcoal, kerosene, petrol,
diesel, liquified petroleum gas (LPG), compressed
natural gas (CNG) etc.
Wood Coal LPG Kerosene
2) Combustion :-
The chemical process in which a substance reacts with
oxygen to produce heat is called combustion.
The substance which undergoes combustion is called a
combustible substance. It is also called a fuel.
Sometimes light is also produced during combustion
either as a flame or as a glow.
Air is necessary for combustion.
3) Air is necessary for burning :-
(a) (b) (c)
Fix a lighted candle on a table. Put a glass chimney over the table and rest
it on a few wooden blocks in such a way so that air can enter the chimney.
Observe what happens to the flame.
Now remove the blocks and let the chimney rest on the table. Again
observe the flame.
Then put a glass plate over the chimney. Observe the flame again.
The candle burns freely in (a) because air enters the chimney from below.
The candle stops burning in (b) because air does not enter the chimney
from below.
The candle does not burn in (c) because air is not available.
This shows that air is necessary for burning.
4) Ignition temperature :-
The minimum temperature at which a substance catches fire and
burns is called its ignition temperature.
A substance will not catch fire and burn if its temperature is lower
than its ignition temperature.
Different substances have different ignition temperatures.
Eg:- The ignition temperature of kerosene is less than the ignition
temperature of wood.
Substances which have very low ignition temperature and can easily
catch fire with a flame are called inflammable substances. Eg:- petrol,
alcohol, LPG, CNG etc.
Read MoreFAQs on PPT - Combustion & Flame
| 1. What is combustion and why does flame need oxygen to burn? |  |
Ans. Combustion is a chemical reaction where a substance reacts with oxygen, releasing heat and light energy. Oxygen acts as a supporter of combustion, meaning flames cannot exist without it-oxygen feeds the burning process by combining with fuel molecules, producing carbon dioxide, water, and energy. This is why fires are extinguished when oxygen supply is cut off.
| 2. How do you identify the difference between rapid combustion and spontaneous combustion in real life? | |
Ans. Rapid combustion occurs quickly with visible flames, like burning wood or petrol, and requires an initial heat source. Spontaneous combustion ignites without an external source-the substance self-heats due to internal chemical reactions, such as wet hay or phosphorus in air. The key distinction: rapid combustion needs ignition; spontaneous combustion generates its own ignition temperature naturally.
| 3. What are the three things needed for a flame to start and keep burning? | |
Ans. The fire triangle consists of three essential requirements: fuel (combustible material), oxygen (supporter), and heat (ignition source). All three must be present simultaneously for combustion and flame to occur. Removing any one element-by cooling, suffocating oxygen, or removing fuel-extinguishes the flame. This principle explains how firefighters control and prevent fires effectively.
| 4. Why does a candle flame have different coloured zones, and what do they mean? | |
Ans. A candle flame displays distinct zones because of incomplete and complete combustion at different temperatures. The dark innermost zone contains unburnt wax vapour; the bright yellow middle zone has incomplete combustion producing carbon particles; the blue outer zone represents complete combustion with the highest temperature. Each zone's colour indicates the fuel burn rate and oxygen availability at that location.
| 5. What's the difference between combustible and non-combustible materials, and can you give Class 8 examples? | |
Ans. Combustible materials burn readily in the presence of oxygen and heat-examples include wood, paper, petrol, and natural gas. Non-combustible materials resist burning, such as metals, glass, water, and stone. Understanding this distinction helps students recognise fire hazards and select safe materials for storage. For CBSE Class 8 Science Olympiad preparation, flashcards and PPTs on combustion types help reinforce material classification effectively.
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