In the given reactions, the compounds are undergoing halogenation to form new compounds.

C2H4 -> C2H5Cl: Ethene (C2H4) is reacting with chlorine to form chloroethane (C2H5Cl).C2H6 -> C2H2: Ethane (C2H6) is undergoing dehydrohalogenation to form ethyne (C2H2).