6. Thermodynamics and Kinetics

The reaction of chloromethane with hydroxide ion at 30 °C has a ΔG° value of −21.7 kcal/mol. What is the equilibrium constant for the reaction?

For the following acid–base reactions studied in Assessment 5.25, draw a likely transition state. Be sure to indicate in your drawing the degree to which bonds are broken or formed.

(b)

Calculate the percentage of isopropylcyclohexane molecules that have the isopropyl substituent in an equatorial position at equilibrium. (Its ∆G° value at 25 °C is -2.1 kcal/mol.)

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

(b)

a. For a reaction with ∆H° = -12 kcal/mol and ∆S° = 0.01 kcal mol^-1 K^-1, calculate the ∆G° and the equilibrium constant at:

1. 30 °C and 2. 150 °C.

b. How does ∆G° change as T increases?

c. How does K_eq change as T increases?

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

The relative rate of reaction for the cis alkene (E) is given in Table 22.2. What do you expect the relative rate of reaction for the trans alkene to be?

In light of your answers to parts (b) and (c), where both were shown to be quite favorable, imagine a scenario where either reaction is possible. Of the two, which would you expect to be faster? Which would you expect to be more favored? Explain each in the context of the important thermodynamic and/or kinetic parameters.

The following reaction has a value of ΔG° = –2.1 kJ/mol (–0.50 kcal/mol).

CH₃Br + H₂S ⇌ CH₃SH + HBr

b. Starting with a 1 M solution of CH3Br and H2S, calculate the final concentrations of all four species at equilibrium.

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)

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)

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

(c)

Under base-catalyzed conditions, two molecules of acetone can condense to form diacetone alcohol. At room temperature (25 °C), about 5% of the acetone is converted to diacetone alcohol. Determine the value of ΔG° for this reaction.