Which substance, ethane or chloroethane, is easier to chlorinate and why?

Chlorination of chloroethane will be easier than ethane, since chloroethane already contains a chlorine molecule, to which the electron density will be shifted. Accordingly, the carbon-chlorine bond is more polar, which allows the chlorination of chloroethane to proceed faster.
Ethane chlorination will be a little more complicated according to the following scheme: the chlorine molecule decomposes into radicals that interact with ethane molecules, taking away a hydrogen atom from them, as a result of which ethyl radicals • С2Н5 are formed, and they, in turn, destroy chlorine molecules, forming new radicals … The chlorination reaction is possible until complete replacement of hydrogen.