Textbook Question
Use the information in Table 4-2 (p. 167) to rank the following radicals in decreasing order of stability.
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Ch.4 - The Study of Chemical Reactions
Wade9th EditionOrganic ChemistryISBN: 9780135213728
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Table of contents
- Ch.1 - Structure and Bonding107
- Ch. 2 - Acids and Bases; Functional Groups115
- Ch.3 - Structure and Stereochemistry of Alkanes100
- Ch.4 - The Study of Chemical Reactions99
- Ch.5 - Stereochemistry93
- Ch.6 - Alkyl Halides; Nucleophilic Substitution118
- Ch. 7 - Structure and Synthesis of Alkenes; Elimination158
- Ch.8 - Reactions of Alkenes171
- Ch.9 - Alkynes91
- Ch.10 - Structure and Synthesis of Alcohols143
- Ch.11 - Reactions of Alcohols104
- Ch. 12 - Infrared Spectroscopy and Mass Spectrometry22
- Ch. 13 - Nuclear Magnetic Resonance Spectroscopy45
- Ch. 14 - Ethers, Epoxides, and Thioethers72
- Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy89
- Ch. 16 - Aromatic Compounds74
- Ch. 17 - Reactions of Aromatic Compounds126
- Ch. 18 - Ketones and Aldehydes193
- Ch. 19 - Amines129
- Ch. 20 - Carboxylic Acids77
- Ch. 21 - Carboxylic Acid Derivatives141
- Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds175
- Ch. 23 - Carbohydrates and Nucleic Acids93
- Ch. 24 - Amino Acids, Peptides, and Proteins54
Chapter 4, Problem 41d
Use bond-dissociation enthalpies (Table 4-2, p. 167) to calculate values of ΔH° for the following reactions.
d. CH3CH2CH3 + H2 → CH3CH3 + CH4
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Identify the bonds broken and formed in the reaction. In this case, the bonds broken are one C-H bond in CH3CH2CH3 (propane) and one H-H bond in H2. The bonds formed are one C-H bond in CH3CH3 (ethane) and one C-H bond in CH4 (methane).
Refer to the bond-dissociation enthalpy table (TABLE 4-2, p. 167) to find the bond-dissociation enthalpy values for each bond involved. For example, the bond-dissociation enthalpy for a C-H bond and an H-H bond will be listed in the table.
Calculate the total energy required to break the bonds. This is done by summing the bond-dissociation enthalpy values for the bonds broken (C-H in propane and H-H in H2).
Calculate the total energy released when the new bonds are formed. This is done by summing the bond-dissociation enthalpy values for the bonds formed (C-H in ethane and C-H in methane).
Determine the overall enthalpy change (ΔH°) for the reaction by subtracting the total energy released (bonds formed) from the total energy required (bonds broken). Use the formula: ΔH° = 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.
Bond-Dissociation Enthalpy
Bond-dissociation enthalpy (BDE) is the energy required to break a specific bond in a molecule, resulting in the formation of free 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 expressed in kilojoules per mole (kJ/mol) and vary depending on the type of bond and the molecular environment.
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How to calculate enthalpy using bond dissociation energies.
Enthalpy Change (ΔH°)
The enthalpy change (ΔH°) of a reaction is the difference in enthalpy between the products and reactants under standard conditions. It indicates whether a reaction is exothermic (releases heat, ΔH° < 0) or endothermic (absorbs heat, ΔH° > 0). Calculating ΔH° using bond-dissociation enthalpies involves summing the BDEs of bonds broken in the reactants and subtracting the BDEs of bonds formed in the products.
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Reaction Mechanism
A reaction mechanism describes the step-by-step sequence of elementary reactions by which overall chemical change occurs. Understanding the mechanism is essential for predicting the products and energy changes in a reaction. In the context of the given reaction, recognizing the bonds involved and their respective BDEs allows for accurate calculation of the overall enthalpy change, reflecting the energy dynamics of the process.
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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.
a. CH3—CH3 + I2 → CH3CH2I + HI
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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
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Textbook Question
For each alkane,
1. draw all the possible monochlorinated derivatives.
a. Cyclopentane
b. Methylcyclopentane
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Textbook Question
For each alkane,
2. determine whether free-radical chlorination would be a good way to make any of these monochlorinated derivatives. Will the reaction give mostly one major product?
a. Cyclopentane
b. Methylcyclopentane
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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
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