Question

What is pyrolysis or cracking? Explain with examples.

Answer 1

Hint: Various types of chemical reactions exist that are facilitated by the presence of a particular chemical reagent or any catalyst that provides surface area for the reaction. Pyrolysis is a type of chemical reaction in which the heat supplied acts as the reagent.

Complete answer:
Organic compounds that are formed from strong covalent bonds do not dissociate into their ions or melt very easily. When these compounds (usually having long parent chains and high molecular mass) are strongly heated, they decompose into smaller fragments that have lesser molecular weights and short chains and are usually volatile in nature and can therefore escape as gases or vapours.
This thermal decomposition of organic molecules into smaller fragments is known as Pyrolysis. The term pyrolysis in itself explains its meaning as it is a Greek word consisting of two segments namely ‘pyro’ that stands for fire and ‘lysis’ that stands for segregating.
One important property of pyrolysis or cracking reaction is that it is carried out in the absence of air. The air can supply oxygen and heating organic molecules in the presence of oxygen may lead to a combustion reaction instead of decomposition.
A good example of pyrolysis is the breakdown of high alkanes into smaller chains shows as follows:
\[{C_3}{H_8}\xrightarrow{{heat}}{C_2}{H_4} + C{H_4}\]

Note:
Chemical reactions that accept heat as a reactant or absorb heat during the reaction are known as endothermic reactions. And the chemical reactions that release heat as part of the product during the reaction are called exothermic reactions. Pyrolysis is an example of endothermic reaction.