Textbook Question
Keto–enol tautomerism is a reaction we discuss in detail in Chapter 19. Estimate the equilibrium constant of this reaction (BDE for C―C π bond = 65 kcal/mol ; for C―O π bond = 85 kcal/mol).
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Ch. 5 - Chemical Reaction Analysis: Thermodynamics and Kinetics
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471
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Table of contents
- Ch. 2 - General Chemistry Translated: Finding the Electrons114
- Ch. 3 - Alkanes and Cycloalkanes: Properties and Conformational Analysis109
- Ch. 4 - Acids and Bases: Electron Flow144
- Ch. 5 - Chemical Reaction Analysis: Thermodynamics and Kinetics118
- Ch. 6 - Stereoisomerism: Arrangement of Atoms in Space112
- Ch. 7 - Principles of Green (Organic) Chemistry3
- Ch. 8 - Alkenes I: Properties and Electrophilic Additions158
- Ch. 9 - Alkenes II: Oxidation and Reduction150
- Ch. 10 - Alkynes: Electrophilic Addition and Redox Reactions101
- Ch. 11 - Properties and Synthesis of Alkyl Halides: Radical Reactions108
- Ch. 12 - Substitution and Elimination: Reactions of Haloalkanes172
- Ch. 13 - Alcohols, Ethers and Related Compounds: Substitution and Elimination239
- Ch. 14 - Structural Identification I: Infrared Spectroscopy and Mass Spectrometry54
- Ch. 15 - Structural Identification II: Nuclear Magnetic Resonance Spectroscopy93
- Ch. 16 - Metals in Organic Chemistry48
- Ch. 17 - Carbonyl Addition Reactions: Aldehydes and Ketones45
- Ch. 18 - Nucleophilic Acyl Substitution I: Carboxylic Acids18
- Ch. 19 - Nucleophilic Acyl Substitution II: Carboxylic Acid Derivatives39
- Ch. 20 - Enolates: Carbonyl Addition and Substitution13
- Ch. 21 - Conjugated Systems I: Stability and Addition Reactions56
- Ch. 22 - Conjugated Systems II: Pericyclic Reactions54
- Ch. 23 - Benzene I: Aromatic Stability and Substitution Reactions64
- Ch. 24 - Benzene II: Reactions Influenced by the Aromatic Ring62
- Ch. 25 - Amines: Structure, Reactions, and Synthesis27
- Ch. 26 - Amino Acids, Proteins, and Peptide Synthesis9
- Ch. 27 - Carbohydrates, Nucleic Acids, and Lipids54
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook
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Mullins 1st EditionCh. 5 - Chemical Reaction Analysis: Thermodynamics and KineticsProblem 59c
Mullins 1st EditionCh. 5 - Chemical Reaction Analysis: Thermodynamics and KineticsProblem 59cChapter 4, Problem 59c
Reaction (c), on the other hand, is favored (∆G° < 0). Identify the bonds formed and broken and explain this result in light of (a) and (b).
(c) 
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Identify the bonds broken and formed in reaction (c). For example, analyze the reactants and products to determine which bonds are cleaved and which new bonds are created. Use structural formulas to visualize this process.
Recall that the Gibbs free energy change (∆G°) is related to the bond energies of the bonds broken and formed. Breaking bonds requires energy (endothermic), while forming bonds releases energy (exothermic).
Compare the bond energies of the bonds broken and formed. If the bonds formed are stronger (have higher bond energy) than the bonds broken, the reaction will release energy, making ∆G° negative and the reaction thermodynamically favorable.
Relate this result to reactions (a) and (b). Consider whether the same types of bonds are involved and whether the energy changes in (c) are consistent with the trends observed in (a) and (b).
Conclude by explaining why reaction (c) is favored (∆G° < 0) based on the net energy change from bond breaking and forming, and how this aligns with the thermodynamic principles of exergonic reactions.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Gibbs Free Energy (∆G)
Gibbs Free Energy (∆G) is a thermodynamic potential that measures the maximum reversible work obtainable from a thermodynamic system at constant temperature and pressure. A negative value of ∆G (∆G° < 0) indicates that a reaction is spontaneous, meaning it can occur without external energy input. Understanding this concept is crucial for analyzing the favorability of chemical reactions and predicting their direction.
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Breaking down the different terms of the Gibbs Free Energy equation.
Bond Formation and Breaking
In chemical reactions, bonds between atoms are either formed or broken, which directly influences the energy changes in the system. When bonds are formed, energy is released, contributing to a negative ∆G, while breaking bonds requires energy input. Identifying which specific bonds are involved in the reaction helps in understanding the overall energy dynamics and the reaction's favorability.
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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 transform into products, including the intermediates formed and the transition states. Analyzing the mechanism helps explain why certain reactions are favored or not, particularly in relation to the energy changes associated with bond formation and breaking.
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Related Practice
Textbook Question
Calculate ∆H° for the following alkene addition reaction, one we discuss further in Chapter 7. Predict the sign of ∆S° . (The BDE for C―C π bond is approximately 65 kcal/mol.)
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Textbook Question
The hydrogenation of alkenes is a reaction we study in Chapter 9.
(b) Is this reaction favored or disfavored in terms of entropy?
Textbook Question
(b) Mechanistically, the reaction occurs as shown below. Why is this reaction favored? Based on the stability of the anions, estimate Keq.
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Textbook Question
Calculate Keq for the following acid–base reaction.
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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)
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