XII Chemistry BIEK Topic - Cracking Or Pyrolysis (Short Note)

Cracking Or Pyrolysis (Short Note)
Definition
The phenomenon in which large molecules of hydrocarbons are thermally decomposed into smaller molecules in the absence of air or oxygen is known as Cracking or Pyrolysis.




Examples of Cracking
Cracking can be explained with the help of following examples.


1. Methane

When methane is burnt in absence of air then cracking takes place, as a result carbon black and hydrogen are formed.


2. Gasoline

The most important fraction of petroleum is gasoline (petrol) which is used as motor fuel. The fractional distillation of petroleum yields only a small percentage of total petrol demand. The additional quantity of petrol is obtained by the cracking of diesel.

The large less volatile molecules of diesel that have high boiling point are heated in the absence of air using a catalyst. As a result, cracking takes place and smaller more volatile molecules of petrol having lower boiling point are obtained.

Thus cracking is applied to obtain additional amount of gasoline from crude oil. In cracking a number of other useful by products are also obtained.