6. Thermodynamics and Kinetics

For the following values of ∆H° , ∆S°, and T, tell whether the process would be favored.

(b) ∆H° = +7.34 kcal/mol ; ∆S° = +43 cal/mol•K ; T = 325 K

For each of the following processes, indicate whether you expect ∆S° to be greater than, less than, or equal to 0. Explain your answer.

(c)

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.

When ethene is treated in a calorimeter with H₂ and a Pt catalyst, the heat of reaction is found to be –137 kJ/mol (–32.7 kcal/mol), and the reaction goes to completion. When the reaction takes place at 1400 K, the equilibrium is found to be evenly balanced, with K_eq =1.  Compute the value of ΔS for this reaction.

a. Which of the following reactions has the larger ∆S° value?

b. Is the ∆S° value positive or negative?

The hydrogenation of alkenes is a reaction we study in Chapter 9.

(b) Is this reaction favored or disfavored in terms of entropy?

Would you expect ∆S to be greater than, less than, or equal to zero in the following reactions?

(b)

Would you expect ∆S to be greater than, less than, or equal to zero in the following reactions?

a.

Through the course of this chapter, we have discussed only alkane chlorination and bromination, yet there are two other halogens we have not discussed.

(b) Is radical iodination a favorable reaction? Do you expect it to be selective? Show your calculations.

When ethene is mixed with hydrogen in the presence of a platinum catalyst, hydrogen adds across the double bond to form ethane. At room temperature, the reaction goes to completion. Predict the signs of ΔH° and ΔS° for this reaction. Explain these signs in terms of bonding and freedom of motion.

For each of the following processes, indicate whether you expect ∆S° to be greater than, less than, or equal to 0. Explain your answer.

(b) 2 C₆H₁₄(l) + 19 O₂(g) → 12 CO₂(g) + 14 H₂O(g)

For each of the following processes, indicate whether you expect ∆S° to be greater than, less than, or equal to 0. Explain your answer.

(a) Boiling water

For each reaction, estimate whether ΔS° for the reaction is positive, negative, or impossible to predict.

(a)

At what temperature does the entropy change of a process not contribute to the favorability of a process?

The dehydrogenation of butane to trans-but-2-ene has ΔH° = +116 kJ/mol (+27.6 kcal/mol) and ΔS° = +117J/kelvin-mol (+28.0 cal/kelvin-mol).

a. Compute the value of ΔG° for dehydrogenation at room temperature (25 °C or 298 °K). Is dehydrogenation favored or disfavored?

HINT: When you are doing synthesis problems, avoid using these high-temperature industrial methods. They require specialized equipment, and they produce variable mixtures of products.