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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7:43 minutes

Problem 41b

Textbook Question

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.

Verified step by step guidance

Step 1: Analyze the reaction provided in the image. The reactants are tert-butyl hypochlorite (C4H9OCl) and isobutane (C4H10), and the products are tert-butyl alcohol (C4H9OH) and tert-butyl chloride (C4H9Cl). This reaction involves bond dissociation and formation.

Step 2: Write the bond dissociation and formation processes. Bonds broken: C−H (from isobutane), O−Cl (from tert-butyl hypochlorite). Bonds formed: O−H (in tert-butyl alcohol), C−Cl (in tert-butyl chloride).

Step 3: Use the enthalpy change formula for the reaction: ∆H° = Σ(Bonds broken) − Σ(Bonds formed). Substitute the given values: ∆H° = -42 kcal/mol, bond dissociation enthalpies for C−H = 101 kcal/mol, C−Cl = 85 kcal/mol, O−H = 105 kcal/mol.

Step 4: Rearrange the formula to solve for the bond dissociation enthalpy of O−Cl. Let the bond dissociation enthalpy of O−Cl be x. The equation becomes: -42 = (101 + x) − (85 + 105).

Step 5: Simplify the equation to isolate x. Perform algebraic manipulation to calculate the bond dissociation enthalpy of O−Cl.

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Key Concepts

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

Bond Dissociation Enthalpy (BDE)

Bond dissociation enthalpy is the energy required to break a specific bond in a molecule, resulting in the formation of free radicals. It is typically expressed in kcal/mol and reflects the strength of the bond; higher values indicate stronger bonds. Understanding BDE is crucial for predicting reaction pathways and the stability of intermediates in organic reactions.

Enthalpy Change (∆H°)

Enthalpy change (∆H°) is the heat content change associated with a chemical reaction at constant pressure. A negative ∆H° indicates that the reaction is exothermic, releasing energy, while a positive ∆H° signifies an endothermic reaction, absorbing energy. This concept is essential for calculating the overall energy changes in reactions, including bond formation and breaking.

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 are converted into products, including the formation and breaking of bonds. Understanding the mechanism is vital for predicting the products of a reaction and calculating the associated energy changes, such as bond dissociation enthalpies.

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Related Practice

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?

Textbook Question

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

(b)

Textbook Question

(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?

Textbook Question

Calculate ∆H° for the following reactions.

(b) CH₃Br + HCl → CH₃Cl + HBr

Textbook Question

Calculate ∆H° for the following reactions.