Textbook Question
Label each hydrogen atom in the following compounds as primary (1°), secondary (2°), or tertiary (3°).
(e)
(f)
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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 41a
Use bond-dissociation enthalpies (Table 4-2, p. 167) to calculate values of ΔH° for the following reactions.
a. CH3—CH3 + I2 → CH3CH2I + HI
Verified step by step guidance1
Step 1: Understand the problem. The goal is to calculate the enthalpy change (ΔH°) for the given reaction using bond-dissociation enthalpies. Bond-dissociation enthalpy is the energy required to break a bond in a molecule into its individual atoms in the gas phase.
Step 2: Write down the bonds broken and formed in the reaction. In the given reaction, the bonds broken are one C-H bond in CH3—CH3 and one I-I bond in I2. The bonds formed are one C-I bond in CH3CH2I and one H-I bond in HI.
Step 3: Use the bond-dissociation enthalpy table to find the values for each bond. Look up the bond-dissociation enthalpy for C-H, I-I, C-I, and H-I bonds in the provided table (TABLE 4-2, p. 167). Ensure you use the correct values for each bond.
Step 4: Calculate the total energy required to break the bonds. Add the bond-dissociation enthalpies for the bonds broken (C-H and I-I). This represents the energy input for the reaction.
Step 5: Calculate the total energy released when new bonds are formed. Add the bond-dissociation enthalpies for the bonds formed (C-I and H-I). Subtract the energy released from the energy input to determine ΔH° for the reaction.
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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.
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How to calculate enthalpy using bond dissociation energies.
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).
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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 helps in predicting the products and the energy changes involved. In the given reaction, the mechanism involves the breaking of C-H and I-I bonds and the formation of C-I and H-I bonds, which is essential for calculating the overall enthalpy change.
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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.
c. (CH3)3C—OH + HCl → (CH3)3C—Cl + H2O
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Textbook Question
Label each hydrogen atom in the following compounds as primary (1°), secondary (2°), or tertiary (3°).
(a) CH3CH2CH(CH3)2
(b) (CH3)3CCH2CH3
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Textbook Question
Label each hydrogen atom in the following compounds as primary (1°), secondary (2°), or tertiary (3°).
(c) (CH3)2CHCH(CH3)CH2CH3
(d)
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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
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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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