Combustion
Combustion is the reaction of a substance with oxygen that releases heat. It is an oxidation reaction. To take place, fuel and an oxidising agent are necessary. The burned substance is called fuel, and during combustion, O2 combines with another molecule to produce an oxide.
Examples of combustible and non-combustible matter.
Matters which rapidly burn are combustible substances like LPG, coal, wood, petrol, etc. Matters that slowly or don't but are non-combustible substances like glass, water, sand, stone, etc.
Flame
In combustion, the visible part of it is called flame. The word flame is derived from the Latin word 'flamma'. In the reaction, the fuel reacts with O2 and m es an enormous amount of heat energy. Due to this, atoms get superheated. Now, these atoms want to leave the combustion zone; they emit energy in the form of flame.
Flame is divided into three parts:
- Inner part: Part closest to the wick. It is the least hot part. It contains unburnt particles of the flame.
- Middle part: Large part of the flame. It shows colours like yellow and orange. This part emits light.
- Outer part: The hottest part of the flame with an unlimited supply of O2. It is blue.
Combustion and Flame Sample Questions for Class 8
Question 1
The type of combustion in which heat, light and sound are produced is:
A. rapid
B. explosive
C. spontaneous
D. none of these
Question 2
The metallic cylinder in soda-acid extinguisher contains:
A. NaOH
B. NaHCO3
C. Al (OH)3
D. KOH
Question 3
Acid rain is caused by:
A. deforestation
B. CO2
C. CO
D. oxides of sulphur and nitrogen
Question 4
Match column 'A' with column 'B' as regard to characteristics of a flame and its zones.
A. A-1, B-2, C-3, D-4
B. A-2,B-3,C-4, D-1
C. A-3, B-4, C-2, D-1
D. A-4, B-1, C-2, D-3
Question 5
Which of the following is an ideal fuel?
A. Coal
B. LPG
C. Petrol
D. None of these