Question

Why do we crack molecules?

Answer 1

Cracking is the process whereby complex organic molecules such as kerogens or long chain hydrocarbons are broken down into simpler molecules such as light hydrocarbons,. 
it is done to get more important substances

Answer 2

We need to crack molecules in order for us to get the desired molecule. For example, in the extraction of crude oil, after entering the fractional distillation, it will give products base on their molecular structure. The products are gasoline, diesel fuel, jet fuel, wax, asbestos,kerosene.