Hydrocarbons: describe question

Alkanes can be produced from different sources and undergo various reactions. Describe each of the following:

(i) the reagents and conditions required to convert ethene into ethane by hydrogenation, (ii) how cracking of a long-chain alkane produces more useful alkanes and alkenes, (iii) the mechanism of the free-radical substitution of ethane with chlorine, including the initiation, propagation, and termination steps, (iv) why alkanes are generally unreactive towards polar reagents, (v) the environmental problems caused by the combustion of alkanes in internal combustion engines and how these are reduced.