(i) Propose a mechanism for the reaction shown below:

(ii) Use the appropriate bond-dissociation enthalpies to find the value of ∆Hº for each step shown in the mechanism you proposed, and calculate the value of ∆Hº for the overall reaction if the bond-dissociation enthalpy for PhCH₂−Br bond is approximately 280 kJ/mol. Are these values appropriate for a rapid free-radical chain reaction?