In the iodination of ethane shown below, tetraiodomethane (CI₄) is used as the source of iodine in the presence of a free-radical initiator such as hydrogen peroxide (H₂O₂).
Propose a mechanism for the reaction, and determine the value of ∆H for each of the steps in your mechanism using the appropriate bond-dissociation energies.

H₃C−CH₃ + CI₄ → H₃C−CH₂I + HCI₃

Despite being generally disfavored (∆G° > 0), the given reaction is favored according to ∆H°. Determine which bonds were broken and formed in the reaction. 

Determine the enthalpy change (∆H°) for the given equilibrium process.

Consider the following reaction:

•CH(CH₃)₂ + HF → (CH₃)₂CH₂ + F•

The activation energy and the heat of reaction (ΔH°) of its reverse reaction are 26.1 kJ/mol (6.24 kcal/mol) and −157 kJ/mol (−37.5 kcal/mol), respectively. Determine the activation energy and the heat of reaction (ΔH°) for the forward reaction.

(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?

Which radical is more stable in terms of bond-dissociation energy? Rationalize the difference in stability based on their structures.

Tributyltin hydride (Bu₃SnH) can be used to synthetically reduce alkyl halides. In this process, a halogen atom is replaced by a hydrogen atom. Suggest a mechanism for the initiation and propagation steps for the reaction below. 

Using the following bond-dissociation enthalpies, calculate the values of ΔH for the proposed steps and determine whether each step is energetically favorable.