Class 8, Science, Chapter-4, Lecture-2, Flame (Notes)
Methane has Higher Calorific Value Amongst all Hydrocarbons.
Reason:
Methane has highest percentage of hydrogen amongst all hydrocarbons.
Compounds containing Oxygen have Lower Calorific Value.
Reason:
The presence of oxygen, which is non-combustible, reduces the percentage of hydrogen atoms present in the compound.
Wood Has Lower Calorific Value.
Reason:
The presence of oxygen in wood reduces the percentage of hydrogen in wood.
FLAME:
The hot luminous region where combustion of gases take place is called the Flame.
Two types of Flames:
- Luminous Flame
- Non-luminous Flame
Zones of a Flame:
- Blue Zone (outer zone) – Hottest due to complete combustion
- Yellow Zone (middle zone) – due to glowing of unburnt carbon particles.
- Black Zone (innermost zone) – due to presence of unburnt carbon particles.
Differences Between:
Luminous Flame | Non-Luminous Flame |
---|---|
1. Yellow in colour. | 1. Blue in colour. |
2. Incomplete combustion takes place. | 2. Complete combustion. |
3. Less hot. | 3. Hotter. |
The Flame of a Wick Stove is Blue, but the Flame of a Lamp is Yellow.
Reason:
In a wick stove kerosene burns with a blue flame due to sufficient supply of oxygen but in a lamp insufficient supply of air make the flame yellow.
CHARACTERISTICS OF AN IDEAL FUEL:
- High calorific value.
- Proper ignition temperature.
- Moderate rate of combustion.
- Absence of poisonous gases on combustion.
- Absence of residue on combustion.
- Cheap availability.
- Plentiful availability.
- Ease of storage and transport.
Pollution Due to Combustion of Fuels:
- Burning of Coal produces CO2, the excess of which may increase greenhouse effect.
- Burning of Petroleum Products produce CO2 and CO which is highly poisonous and may cause death.
- Burning of Petroleum Products also releases unburnt lead particles which are highly poisonous.