6. Thermodynamics and Kinetics

A certain process has ∆H° = 11.7 kcal/mol and AS° = +33cal/mol•K . That is, this reaction has an unfavorable enthalpy but a favorable entropy term. At what temperature will the process be neither favored nor disfavored?

Calculate ∆G°, ∆H°, and ∆S° for the following acid–base reactions. Rationalize the value of ∆H° based on the structure of the conjugate bases. [Assume T = 298 K.]

(a)

Calculate ∆G°, ∆H°, and ∆S° for the following acid–base reactions. Rationalize the value of ∆H° based on the structure of the conjugate bases. [Assume T = 298 K.]

(c)

Write the rate law for the following reaction and identify which molecules are present in the rate-determining step. Draw a possible transition state and propose a mechanism.

Third-order reactions are rare. Why do you think that is?

For the following acid–base reaction, (d) calculate ∆G° at 298 K.

For the following acid–base reaction, (e) calculate ∆G° at 273 K.

For the following acid–base reaction, (f) calculate ∆G° at 373 K.

For each of the following acid–base reactions, (iii) calculate ∆G°. If a pK_a is not one of the ten common ones we learned in Chapter 4, it will be given to you.

(a)

Using the bond-dissociation energies in Table 5.6 (see Section 5.3.1), estimate the equilibrium constant of the following reaction at 298 K.

For the following reactions we have not seen yet, which side, if either, would be favored by increasing the temperature?

(c)

For the following reactions we have not seen yet, which side, if either, would be favored by increasing the temperature?

(d)

For the following equilibrium processes and the corresponding ∆G°, calculate (i) K_eq and (ii) the % composition of the equilibrium mixture (% reactants, % products) at 298 K.

(a)

For the following equilibrium processes and the corresponding ∆G°, calculate (i) K_eq and (ii) the % composition of the equilibrium mixture (% reactants, % products) at 298 K.

(b)

For each pair of reactions, predict which will happen more quickly.

[For (a) and (b), think about the stability of the bases involved.]

(a)