If ΔH° is negative, what does this say about the favorability of a reaction?

Calculate ∆H° for the following equilibrium processes.

(d)

Calculate the ∆H° value for the following reaction:

To this point, hydrogenation has always been an exothermic process. Using the numbers from Fig­ure 21.6, calculate ∆H^o_hydr for each step of the reduction of benzene.

∆H₁ + ∆H₂ + ∆H₃ = ∆H_tot = ―49.5 kcal /mol (―208 kJ/mol)

Predict the sign and magnitude of ∆H^oin kj/mol for the following reaction. Identify the reaction as either exothermic or endothermic.

Iodination of alkanes using iodine (I₂) is usually an unfavorable reaction. (See Problem 4-17 , for example.) Tetraiodomethane (CI₄) can be used as the iodine source for iodination in the presence of a free-radical initiator such as hydrogen peroxide. Propose a mechanism (involving mildly exothermic propagation steps) for the following proposed reaction. Calculate the value of ΔH for each of the steps in your proposed mechanism.

The following bond-dissociation energies maybe helpful: