[jadelamlam]

1.Catalytic cracking produce highly branched hydrocarbons,while thermal
cracking produces unbranched hydrocarbons,can anyone explain?

2.Under some conditions,apart from alkanes and alkenes,hydrogen and
carbon are also formed.Why?
For example:
C14H30 --> C8H18 + 2CH2=CH2 + 2C + 2H2

[AWK]

http://en.wikipedia.org/wiki/Cracking_(chemistry)