6. Thermodynamics and Kinetics

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

c. (CH₃)₃C—OH + HCl → (CH₃)₃C—Cl + H₂O

Teflon-coated frying pans routinely endure temperatures that would cause polyethylene or polypropylene to oxidize and decompose. Decomposition of polyethylene is initiated by free-radical abstraction of a hydrogen atom by O₂. Bond-dissociation energies of C—H bonds are about 400 kJ/mol, and C—F bonds are about 460 kJ/mol. The BDE of the H—OO bond is about 192 kJ/mol, and the F—OO bond is about 63 kJ/mol. Show why Teflon (Figure 7-5) is much more resistant to oxidation than polyethylene is.

Given that ∆H° for the reaction is -42 kcal/mol and the bond dissociation enthalpies for the C−H, C−Cl, and O−H bonds are 101, 85, and 105 kcal/mol respectively, calculate the bond dissociation enthalpy of the O−Cl bond.

Using bond-dissociation energies, identify the most stable radical. Justify the difference in stability based on the structure.

(a)

Keto–enol tautomerism is a reaction we discuss in detail in Chapter 19. Estimate the equilibrium constant of this reaction (BDE for C―C π bond = 65 kcal/mol ; for C―O π bond = 85 kcal/mol).

Without concerning yourself with the mechanism of the reaction, calculate the equilibrium constant for the following equilibrium processes. (Assume T = 298 K.)

(a)

a. Using the BDEs in Table 4-2 (page 167), compute the value of ΔH° for each step in the iodination of methane.

b. Compute the overall value of ΔH° for iodination.

Using bond-dissociation energies, identify the most stable radical. Justify the difference in stability based on the structure.

(d) I• vs •OH

Using bond-dissociation energies, identify the most stable radical. Justify the difference in stability based on the structure.

(c)

(i) Using bond dissociation energies, calculate ∆H° for the following reactions. [BDE for O―H = 110 kcal /mol.]

(b)

(a) Using bond-dissociation energies (Table 5.6), which of the indicated bonds should break most easily?

(b) How does that help you explain the results shown in Figure 11.40?

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

a. Using bond-dissociation enthalpies from Table 4-2. (page 167), calculate the heat of reaction for each step in the free-radical bromination of methane

b. Calculate the overall heat of the reaction.

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

d. CH₃CH₂CH₃ + H₂ → CH₃CH₃ + CH₄