Textbook Question
Is the total enthalpy (H) of the reactants for an endothermic reaction greater than or less than the total enthalpy of the products?
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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 22a
The following diagram portrays a reaction of the type A(s) → B(g) + C(g), where the different-colored spheres represent different molecular structures. Assume that the reaction has ∆H = +9.1 kcal/mol (+38.1 kJ/mol).
a. What is the sign of ∆S for the reaction?
Verified step by step guidance1
Step 1: Analyze the reaction type. The reaction is A(s) → B(g) + C(g), where a solid (A) is breaking down into two gaseous products (B and C). This indicates a phase change from solid to gas, which typically increases disorder in the system.
Step 2: Examine the diagram. On the left side, the solid A is represented as tightly packed spheres, indicating a highly ordered structure. On the right side, the products B and C are represented as dispersed spheres, indicating a less ordered, more random distribution.
Step 3: Recall the concept of entropy (∆S). Entropy is a measure of disorder or randomness in a system. When a solid transitions to gases, the particles gain freedom of movement, leading to an increase in entropy.
Step 4: Consider the number of particles. The reaction produces two gaseous products from one solid reactant. The increase in the number of particles contributes to a higher degree of randomness and thus a positive ∆S.
Step 5: Conclude the sign of ∆S. Based on the increase in disorder and the transition from a solid to gases, the sign of ∆S for this reaction is positive.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Entropy (∆S)
Entropy, denoted as ∆S, is a measure of the disorder or randomness in a system. In chemical reactions, an increase in the number of gas molecules typically leads to an increase in entropy, as gases have more freedom of movement compared to solids. Therefore, understanding how the state of matter changes in a reaction is crucial for determining the sign of ∆S.
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Entropy (Simplified) Concept 2
Phase Changes
Phase changes refer to the transitions between solid, liquid, and gas states of matter. In the given reaction, a solid (A) is converted into two gaseous products (B and C). This transition from a more ordered solid state to a less ordered gaseous state generally results in an increase in entropy, which is essential for predicting the sign of ∆S.
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Thermodynamics of Reactions
Thermodynamics studies the relationships between heat, work, and energy in chemical reactions. The enthalpy change (∆H) and entropy change (∆S) are key components in determining the spontaneity of a reaction. In this case, the positive ∆H indicates that the reaction absorbs heat, but the increase in the number of gas molecules suggests that ∆S is likely positive, which can influence the overall spontaneity of the reaction.
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Related Practice
Textbook Question
The following diagram portrays a reaction of the type A(s) → B(g) + C(g), where the different-colored spheres represent different molecular structures. Assume that the reaction has ∆H = +9.1 kcal/mol (+38.1 kJ/mol).
b. Is the reaction likely to be spontaneous at all temperatures, nonspontaneous at all temperatures, or spontaneous at some but nonspontaneous at others?
Textbook Question
What effect do the listed changes have on the position of the equilibrium in the reaction of carbon with hydrogen?
C(s) + 2 H2(g) ⇌ CH4(g) ∆H = -18 kcal/mol (-75kJ/mol)
b. Increasing pressure by decreasing volume
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Textbook Question
What effect do the listed changes have on the position of the equilibrium in the reaction of carbon with hydrogen?
C(s) + 2 H2(g) ⇌ CH4(g) ∆H = -18 kcal/mol (-75kJ/mol)
c. Allowing CH4 to escape continuously from the reaction vessel
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Textbook Question
The vaporization of Br2 from the liquid to the gas state requires 7.4 kcal/mol (31.0 kJ/mol).
a. What is the sign of ∆H for this process? Write a reaction showing heat as a product or reactant.
Textbook Question
Two curves are shown in the following energy diagram:
b. Which curve represents the spontaneous reaction, and which the nonspontaneous?