A possible reaction of ethane with chlorine is:

CH3CH3 + Cl2 ---> CH3CH2Cl + HCl

This reaction could conceivably occur by the following chain mechanism involving steps [1], [2], [3] and [4]. The chain initiating step(s) is (are):

[1] Cl2 --> 2Cl*
[2] Cl* + CH3CH3 --> HCl + CH3C*H2
[3] CH3C*H2 + Cl2 ---> CH3CH2Cl + Cl*
[4] Cl* + Cl* ---> Cl2