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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Problem 37a

Textbook Question

Calculate ∆H° for the following reactions.
(a)

Verified step by step guidance

Step 1: Identify the bonds broken and formed in the reaction. In the given reaction, bonds in the reactants are broken, and new bonds are formed in the products. Specifically, a C-H bond in CH4 is broken, and a C-H bond in the alkane is formed.

Step 2: Use bond dissociation energy (BDE) values to calculate the energy change for breaking and forming bonds. Bond dissociation energy is the energy required to break a bond. Look up the BDE values for the C-H bond in CH4 and the C-H bond in the alkane.

Step 3: Calculate the total energy required to break the bonds in the reactants. Sum the BDE values for all bonds broken in the reaction.

Step 4: Calculate the total energy released when new bonds are formed in the products. Sum the BDE values for all bonds formed in the reaction.

Step 5: Determine ∆H° for the reaction by subtracting the total energy released (from Step 4) from the total energy required (from Step 3). Use the formula: ∆H° = Σ(Bonds Broken) - Σ(Bonds Formed).

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Key Concepts

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

Enthalpy Change (∆H°)

Enthalpy change (∆H°) is a measure of the heat content of a system at constant pressure. It indicates whether a reaction is exothermic (releases heat, ∆H° < 0) or endothermic (absorbs heat, ∆H° > 0). Calculating ∆H° for a reaction involves determining the difference in enthalpy between products and reactants, often using standard enthalpy values.

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, knowing how the alkene interacts with methane to produce another alkene and hydrogen is crucial for calculating ∆H°.

Bond Energies

Bond energies refer to the amount of energy required to break a bond between two atoms. In thermodynamic calculations, the total energy required to break bonds in the reactants minus the energy released when new bonds form in the products gives the overall enthalpy change. This concept is essential for calculating ∆H° in the provided reaction, as it involves breaking and forming specific bonds.

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Related Practice

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

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.

Textbook Question

Calculate ∆H° for the following reactions.

(b) CH₃Br + HCl → CH₃Cl + HBr

Textbook Question

Calculate ∆H° for the following reactions.