Textbook Question
For the reaction
b. Does entropy increase or decrease in this process?
Ch.7 Chemical Reactions: Energy, Rate and Equilibrium
McMurry8th EditionFundamentals of General, Organic, and Biological ChemistryISBN: 9780134015187
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Table of contents
- Ch.1 Matter and Measurements27
- Ch.2 Atoms and the Periodic Table20
- Ch.3 Ionic Compounds8
- Ch.4 Molecular Compounds23
- Ch.5 Classification & Balancing of Chemical Reactions12
- Ch.6 Chemical Reactions: Mole and Mass Relationships28
- Ch.7 Chemical Reactions: Energy, Rate and Equilibrium64
- Ch.8 Gases, Liquids and Solids24
- Ch.9 Solutions52
- Ch.10 Acids and Bases25
- Ch.11 Nuclear Chemistry22
- Ch.12 Introduction to Organic Chemistry: Alkanes57
- Ch.13 Alkenes, Alkynes, and Aromatic Compounds47
- Ch.14 Some Compounds with Oxygen, Sulfur, or a Halogen50
- Ch.15 Aldehydes and Ketones45
- Ch.16 Amines42
- Ch.17 Carboxylic Acids and Their Derivatives57
- Ch.18 Amino Acids and Proteins82
- Ch.19 Enzymes and Vitamins63
- Ch.20 Carbohydrates44
- Ch.21 The Generation of Biochemical Energy65
- Ch.22 Carbohydrate Metabolism45
- Ch.23 Lipids42
- Ch.24 Lipid Metabolism33
- Ch.25 Protein and Amino Acid Metabolism24
- Ch.26 Nucleic Acids and Protein Synthesis45
McMurry8th EditionFundamentals of General, Organic, and Biological ChemistryISBN: 9780134015187Not the one you use?Change textbook
Chapter 7, Problem 36
Under what conditions might a reaction be endothermic but exergonic? Explain.
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Understand the key terms: An endothermic reaction absorbs heat from the surroundings (ΔH > 0), while an exergonic reaction is spontaneous, meaning it has a negative Gibbs free energy change (ΔG < 0).
Recall the Gibbs free energy equation: , where ΔG is the Gibbs free energy change, ΔH is the enthalpy change, T is the temperature in Kelvin, and ΔS is the entropy change.
Analyze the relationship between the terms: For a reaction to be endothermic (ΔH > 0) but still exergonic (ΔG < 0), the term must be large enough to outweigh the positive ΔH. This means the entropy change (ΔS) must be positive and significant, and the temperature (T) must be high.
Consider the physical meaning: A positive ΔS indicates an increase in disorder or randomness in the system, such as when a solid dissolves into a liquid or a liquid evaporates into a gas. At high temperatures, the contribution of becomes more dominant in the Gibbs free energy equation.
Conclude the conditions: A reaction can be endothermic but exergonic if it has a large positive entropy change (ΔS > 0) and occurs at a sufficiently high temperature (T), ensuring that the term outweighs the positive ΔH.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Endothermic Reactions
Endothermic reactions are chemical processes that absorb heat from their surroundings, resulting in a decrease in temperature of the environment. This occurs when the energy required to break bonds in the reactants exceeds the energy released when new bonds form in the products. A common example is the dissolution of ammonium nitrate in water, which absorbs heat and feels cold.
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Endothermic & Exothermic Reactions
Exergonic Reactions
Exergonic reactions are those that release free energy, making them spontaneous under certain conditions. The Gibbs free energy change (ΔG) for these reactions is negative, indicating that the products have lower energy than the reactants. An example is the combustion of glucose, which releases energy that can be harnessed for biological processes.
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Gibbs Free Energy
Gibbs free energy (G) is a thermodynamic potential that helps predict the direction of chemical reactions. It combines enthalpy (heat content) and entropy (disorder) to determine whether a reaction is spontaneous. A reaction can be endothermic (positive ΔH) yet exergonic (negative ΔG) if the increase in entropy (ΔS) is significant enough to offset the heat absorbed, allowing the reaction to proceed spontaneously.
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Related Practice
Textbook Question
For each of the following processes, specify whether entropy increases or decreases. Explain each of your answers.
a. Assembling a jigsaw puzzle
Textbook Question
What two factors affect the spontaneity of a reaction?
Textbook Question
For the reaction 2 Hg(l) + O2(g) → 2 HgO(s), ∆H = –43 kcal/mol (–180 kJ/mol).
a. Does entropy increase or decrease in this process? Explain.
Textbook Question
For the reaction 2 Hg(l) + O2(g) → 2 HgO(s), ∆H = –43 kcal/mol (–180 kJ/mol).
b. Under what conditions would you expect this process to be spontaneous?
Textbook Question
What is the difference between an exothermic reaction and an exergonic reaction?