In catalytic cracking - C2H6 ---> C2H4 + H2 In this reaction C2H6 is heated 750*C-1000*C. Then why it does not convert into 2C + 3H2 ? as CH4 convert into C + 2H2 .

The alkanes , on heating under high temperature or in the presence of catalyst in absence of air are broken down into lower alkanes,alkenes and hydrogen.

 

Methane on cracking breaks down into ethyne and hydrogen.

 

Ethane on cracking breaks down into ethene and hydrogen.