The conversion of CH3Cl to C3H8 to C2H6 involves a series of chemical reactions.

CH3Cl $methylchloride$ can undergo chlorination reactions to form higher hydrocarbons such as C3H8 $propane$. This can happen through a series of steps involving chlorination and subsequent elimination reactions.

C3H8 can then undergo hydrogenation or dehydrogenation reactions to form C2H6 $ethane$. This can involve the addition or removal of hydrogen atoms from the propane molecule.

Overall, the conversion from CH3Cl to C3H8 to C2H6 involves manipulating the carbon and hydrogen atoms in the molecules through chemical reactions.