Reaction (c), on the other hand, is favored (∆G° < 0). Identify the bonds formed and broken and explain this result in light of (a) and (b).
(c)

Use bond-dissociation enthalpies (Table 4-2, p. 167) to calculate values of ΔH° for the following reactions.

d. CH₃CH₂CH₃ + H₂ → CH₃CH₃ + CH₄

If the following reaction is favorable, what can we say about the sign of ∆H°? Explain your answer.

Give the approximate bond-dissociation energy for each indicated bond.

Calculate ∆H° for the following alkene addition reaction, one we discuss further in Chapter 7. Predict the sign of ∆S° . (The BDE for C―C π bond is approximately 65 kcal/mol.)

Calculate ∆H° for the following equilibrium processes.

(b)

The combustion of alkanes is exothermic (∆H° < 0) . Would you expect the combustion of butane or cyclobutane to be more exothermic?

Reactions (a) and (b) are disfavored overall (∆G° > 0), yet they are favored based on ∆H°. Identify the bonds formed and broken for (a) and (b).

(b)

a. Propose a mechanism for the following reaction:

b. Use the bond-dissociation enthalpies given in Table 4-2 (page 167) to calculate the value of ΔH° for each step shown in your mechanism. (The BDE for CH₂=CHCH₂―Br is about 280 kJ/mol, or 67 kcal/mol.) Calculate the overall value of ΔH° for the reaction. Are these values consistent with a rapid free-radical chain reaction?