Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

6. Thermodynamics and Kinetics

Enthalpy

Organic Chemistry

6. Thermodynamics and Kinetics

Enthalpy

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8:35 minutes

Problem 59c

Textbook Question

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)

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Identify the bonds broken and formed in reaction (c). For example, analyze the reactants and products to determine which bonds are cleaved and which new bonds are created. Use structural formulas to visualize this process.

Recall that the Gibbs free energy change (∆G°) is related to the bond energies of the bonds broken and formed. Breaking bonds requires energy (endothermic), while forming bonds releases energy (exothermic).

Compare the bond energies of the bonds broken and formed. If the bonds formed are stronger (have higher bond energy) than the bonds broken, the reaction will release energy, making ∆G° negative and the reaction thermodynamically favorable.

Relate this result to reactions (a) and (b). Consider whether the same types of bonds are involved and whether the energy changes in (c) are consistent with the trends observed in (a) and (b).

Conclude by explaining why reaction (c) is favored (∆G° < 0) based on the net energy change from bond breaking and forming, and how this aligns with the thermodynamic principles of exergonic reactions.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Gibbs Free Energy (∆G)

Gibbs Free Energy (∆G) is a thermodynamic potential that measures the maximum reversible work obtainable from a thermodynamic system at constant temperature and pressure. A negative value of ∆G (∆G° < 0) indicates that a reaction is spontaneous, meaning it can occur without external energy input. Understanding this concept is crucial for analyzing the favorability of chemical reactions and predicting their direction.

Bond Formation and Breaking

In chemical reactions, bonds between atoms are either formed or broken, which directly influences the energy changes in the system. When bonds are formed, energy is released, contributing to a negative ∆G, while breaking bonds requires energy input. Identifying which specific bonds are involved in the reaction helps in understanding the overall energy dynamics and the reaction's favorability.

Reaction Mechanism

A reaction mechanism describes the step-by-step sequence of elementary reactions by which overall chemical change occurs. It provides insight into how reactants transform into products, including the intermediates formed and the transition states. Analyzing the mechanism helps explain why certain reactions are favored or not, particularly in relation to the energy changes associated with bond formation and breaking.

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Related Practice

Textbook Question

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

d. CH₃CH₂CH₃ + H₂ → CH₃CH₃ + CH₄

Textbook Question

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

Textbook Question

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

Textbook Question

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.)

Textbook Question

Calculate ∆H° for the following equilibrium processes.

(b)

Textbook Question

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

Textbook Question

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)

Textbook Question

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?

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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)

Key Concepts

Gibbs Free Energy (∆G)

Bond Formation and Breaking

Reaction Mechanism

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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)