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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4:07 minutes

Problem 41b

Textbook Question

Use bond-dissociation enthalpies (Table 4-2, p. 167) to calculate values of ΔH° for the following reactions.
b. CH₃CH₂Cl + HI → CH₃CH₂I + HCl

Verified step by step guidance

Identify the bonds broken and formed in the reaction. In this case, the bonds broken are the C-Cl bond in CH3CH2Cl and the H-I bond in HI. The bonds formed are the C-I bond in CH3CH2I and the H-Cl bond in HCl.

Look up the bond-dissociation enthalpies (BDEs) for each bond in the reaction. These values can be found in Table 4-2 on page 167. For example, the BDE for a C-Cl bond, H-I bond, C-I bond, and H-Cl bond should be noted.

Calculate the total energy required to break the bonds. This is the sum of the BDEs for the bonds broken: BDE(C-Cl) + BDE(H-I).

Calculate the total energy released when the new bonds are formed. This is the sum of the BDEs for the bonds formed: BDE(C-I) + BDE(H-Cl).

Determine the overall enthalpy change (ΔH°) for the reaction by subtracting the total energy released from the total energy required: ΔH° = [BDE(C-Cl) + BDE(H-I)] - [BDE(C-I) + BDE(H-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

Bond-dissociation enthalpy (BDE) is the energy required to break a specific bond in a molecule, resulting in the formation of two radicals. It is a crucial concept in thermochemistry, as it helps predict the stability of molecules and the energy changes during chemical reactions. BDE values are typically provided in kilojoules per mole (kJ/mol) and vary depending on the type of bond and the molecular environment.

Enthalpy Change (ΔH°)

Enthalpy change (ΔH°) refers to the heat content change of a system at constant pressure during a chemical reaction. It can be calculated using the bond-dissociation enthalpies of the reactants and products. The formula ΔH° = ΣBDE(reactants) - ΣBDE(products) allows chemists to determine whether a reaction is exothermic (releases heat) or endothermic (absorbs heat).

Reaction Mechanism

A reaction mechanism describes the step-by-step sequence of elementary reactions by which overall chemical change occurs. Understanding the mechanism helps in predicting the products and the energy changes involved. In the given reaction, the mechanism involves the breaking of C-Cl and H-I bonds and the formation of C-I and H-Cl bonds, which is essential for calculating the overall enthalpy change.

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Related Practice

Textbook Question

The bromination of methane proceeds through the following steps:

d. Compute the overall value of ΔH° for the bromination

Textbook Question

a. Using bond-dissociation enthalpies from Table 4-2. (page 167), calculate the heat of reaction for each step in the free-radical bromination of methane

b. Calculate the overall heat of the reaction.

Textbook Question

•CH₃ + HCl → CH₄ + Cl•

b. What is the activation energy for this reverse reaction?

c. What is the heat of reaction (ΔH°) for this reverse reaction?

Textbook Question

a. Using the BDEs in Table 4-2 (page 167), compute the value of ΔH° for each step in the iodination of methane.

b. Compute the overall value of ΔH° for iodination.

Textbook Question

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

c. (CH₃)₃C—OH + HCl → (CH₃)₃C—Cl + H₂O

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.

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Use bond-dissociation enthalpies (Table 4-2, p. 167) to calculate values of ΔH° for the following reactions.b. CH3CH2Cl + HI → CH3CH2I + HCl

Key Concepts

Bond-Dissociation Enthalpy

Enthalpy Change (ΔH°)

Reaction Mechanism

Watch next

Use bond-dissociation enthalpies (Table 4-2, p. 167) to calculate values of ΔH° for the following reactions.
b. CH₃CH₂Cl + HI → CH₃CH₂I + HCl