Textbook Question
(a) For a process that occurs at constant temperature, does the change in Gibbs free energy depend on changes in the enthalpy and entropy of the system?
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Ch.19 - Chemical Thermodynamics
Brown15th EditionChemistry: The Central ScienceISBN: 9780137542970
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Table of contents
- Ch.1 - Introduction: Matter, Energy, and Measurement111
- Ch.2 - Atoms, Molecules, and Ions166
- Ch.3 - Chemical Reactions and Reaction Stoichiometry138
- Ch.4 - Reactions in Aqueous Solution127
- Ch.5 - Thermochemistry104
- Ch.6 - Electronic Structure of Atoms109
- Ch.7 - Periodic Properties of the Elements107
- Ch.8 - Basic Concepts of Chemical Bonding102
- Ch.9 - Molecular Geometry and Bonding Theories120
- Ch.10 - Gases122
- Ch.11 - Liquids and Intermolecular Forces79
- Ch.12 - Solids and Modern Materials102
- Ch.13 - Properties of Solutions99
- Ch.14 - Chemical Kinetics153
- Ch.15 - Chemical Equilibrium83
- Ch.16 - Acid-Base Equilibria109
- Ch.17 - Additional Aspects of Aqueous Equilibria117
- Ch.18 - Chemistry of the Environment60
- Ch.19 - Chemical Thermodynamics109
- Ch.20 - Electrochemistry113
- Ch.21 - Nuclear Chemistry79
- Ch.22 - Chemistry of the Nonmetals52
- Ch.23 - Transition Metals and Coordination Chemistry57
- Ch.24 - The Chemistry of Life: Organic and Biological Chemistry7
Brown15th EditionChemistry: The Central ScienceISBN: 9780137542970Not the one you use?Change textbook
Chapter 19, Problem 55b
For a certain chemical reaction, ΔH° = -35.4 kJ and ΔS° = -85.5 J/K. (b) Does the reaction lead to an increase or decrease in the randomness or disorder of the system?
Verified step by step guidance1
Identify the given entropy change, ΔS°, which is -85.5 J/K.
Understand that entropy, represented by 'S', is a measure of the randomness or disorder of a system.
Recognize that a negative ΔS° indicates a decrease in entropy.
Conclude that if ΔS° is negative, the randomness or disorder of the system decreases during the reaction.
Thus, the reaction leads to a decrease in the randomness or disorder of the system.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Enthalpy (ΔH)
Enthalpy is a measure of the total energy of a thermodynamic system, often associated with heat transfer during a reaction at constant pressure. A negative ΔH indicates that the reaction is exothermic, meaning it releases heat to the surroundings. This can influence the spontaneity of a reaction, as exothermic reactions tend to favor product formation.
Entropy (ΔS)
Entropy is a measure of the disorder or randomness in a system. A negative ΔS indicates that the reaction leads to a decrease in disorder, meaning the products are more ordered than the reactants. Understanding entropy is crucial for predicting the spontaneity of reactions, as systems tend to evolve towards higher entropy.
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Entropy in Thermodynamics
Gibbs Free Energy (ΔG)
Gibbs Free Energy combines enthalpy and entropy to determine the spontaneity of a reaction at constant temperature and pressure. The relationship is given by the equation ΔG = ΔH - TΔS. A negative ΔG indicates that a reaction is spontaneous, while a positive ΔG suggests non-spontaneity. In this case, the signs of ΔH and ΔS will help assess the overall spontaneity.
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Related Practice
Textbook Question
Use data in Appendix C to calculate ΔH°, ΔS°, and ΔG° at 25 °C for each of the following reactions.
a. 4 Cr(s) + 3 O2(g) → 2 Cr2O3(s)
b. BaCO3(s) → BaO(s) + CO2(g)
c. 2 P(s) + 10 HF(g) → 2 PF5(g) + 5 H2(g)
d. K(s) + O2(g) → KO2(s)
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Textbook Question
Using S° values from Appendix C, calculate ΔS° values for the following reactions. In each case, account for the sign of ΔS°.
(a) C2H4(g) + H2(g) → C2H6(g)
(b) N2O4(g) → 2 NO2(g)
(c) Be(OH)2(s) → BeO(s) + H2O(g)
(d) 2 CH3OH(g) + 3 O2(g) ⟶ 2 CO2(g) + 4 H2O(g)
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Textbook Question
For a certain chemical reaction, ΔH° = -35.4 kJ and ΔS° = -85.5 J/K. (c) Calculate ΔG° for the reaction at 298 K. (d) Is the reaction spontaneous at 298 K under standard conditions?