Summary class 8 science combustion and flame notes

📘 COMBUSTION AND FLAME – COMPLETE
NOTES

1. Combustion
Definition:
Combustion is a chemical process in which a substance reacts with oxygen to produce heat.
Sometimes light is also produced.

Examples:
Burning of coal, wood, LPG.




2. Conditions Needed for Combustion
A substance will burn only if:

1. There is oxygen
2. The substance is heated to its ignition temperature
3. The substance is inflammable




3. Ignition Temperature
Definition:
The lowest temperature at which a substance catches fire is called its ignition temperature.

Example:

 Paper has low ignition temperature
 Wood has high ignition temperature




4. Inflammable Substances
Substances that catch fire very easily and have low ignition temperature.
Examples: Petrol, LPG, alcohol.




5. Types of Combustion
(i) Rapid Combustion

 Burns quickly
 Produces heat and light
Example: Gas burner.

, (ii) Spontaneous Combustion

 Starts burning on its own
Example: Burning of white phosphorus.

(iii) Explosion

 A lot of gas is released suddenly
 Produces heat, light, and sound
Example: Firecrackers, gunpowder.




6. Flame
The region of burning gas which produces heat and light is called a flame.




7. Structure of a Candle Flame
(i) Outer Zone

 Blue
 Hottest region
 Complete combustion

(ii) Middle Zone

 Yellow
 Moderately hot
 Partial combustion
 Glowing carbon particles → yellow colour

(iii) Inner Zone

 Dark
 Least hot
 Contains unburnt wax vapours
 No combustion




8. Luminous and Non-Luminous Flames
(i) Luminous Flame

 Yellow
 Glows brightly
 Incomplete burning
 Produces soot
 Less hot
Example: Candle flame.

(ii) Non-Luminous Flame