Textbook Question
Consider the gas-phase reaction of AB3 and A2 molecules: (a) Write a balanced equation for the reaction.(b) What is the sign of the entropy change for the reaction?
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Ch.18 - Thermodynamics: Entropy, Free Energy & Equilibrium
McMurry8th EditionChemistryISBN: 9781292336145
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Table of contents
- Ch.1 - Chemical Tools: Experimentation & Measurement143
- Ch.2 - Atoms, Molecules & Ions134
- Ch.3 - Mass Relationships in Chemical Reactions149
- Ch.4 - Reactions in Aqueous Solution157
- Ch.5 - Periodicity & Electronic Structure of Atoms92
- Ch.6 - Ionic Compounds: Periodic Trends and Bonding Theory73
- Ch.7 - Covalent Bonding and Electron-Dot Structures47
- Ch.8 - Covalent Compounds: Bonding Theories and Molecular Structure51
- Ch.9 - Thermochemistry: Chemical Energy104
- Ch.10 - Gases: Their Properties & Behavior138
- Ch.11 - Liquids & Phase Changes43
- Ch.12 - Solids and Solid-State Materials56
- Ch.13 - Solutions & Their Properties98
- Ch.14 - Chemical Kinetics79
- Ch.15 - Chemical Equilibrium107
- Ch.16 - Aqueous Equilibria: Acids & Bases94
- Ch.17 - Applications of Aqueous Equilibria125
- Ch.18 - Thermodynamics: Entropy, Free Energy & Equilibrium66
- Ch.19 - Electrochemistry130
- Ch.20 - Nuclear Chemistry73
- Ch.21 - Transition Elements and Coordination Chemistry122
- Ch.22 - The Main Group Elements155
- Ch.23 - Organic and Biological Chemistry43
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McMurry 8th EditionCh.18 - Thermodynamics: Entropy, Free Energy & EquilibriumProblem 16
McMurry 8th EditionCh.18 - Thermodynamics: Entropy, Free Energy & EquilibriumProblem 16Chapter 18, Problem 16
Consider the following graph of total free energy of reactants and products versus reaction progress for the general reaction, Reactants -> Products. At which of the four points (labeled a, b, c, and d) is Q < K? 
(a) Point a(b) Point c and d(c) Point a, c, and d(d) Point b
Verified step by step guidance1
Identify the points on the graph where the reaction is not at equilibrium. These points are where the reaction quotient Q is not equal to the equilibrium constant K.
Understand that at equilibrium, Q = K, and the system is at its lowest free energy state.
Recognize that points a, b, c, and d are not at equilibrium because they are not at the lowest free energy state (point e).
Determine the direction of the reaction progress. If the reaction proceeds towards products, Q < K; if it proceeds towards reactants, Q > K.
Since points a, c, and d are on the path towards the products (lower free energy), Q < K at these points.
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Gibbs Free Energy (G)
Gibbs Free Energy is a thermodynamic potential that measures the maximum reversible work obtainable from a thermodynamic system at constant temperature and pressure. It is a crucial factor in determining the spontaneity of a reaction; if the change in Gibbs Free Energy (ΔG) is negative, the reaction is spontaneous in the forward direction.
Recommended video:
Guided course
01:51
Gibbs Free Energy of Reactions
Reaction Quotient (Q) and Equilibrium Constant (K)
The reaction quotient (Q) is a measure of the relative concentrations of products and reactants at any point in a reaction, while the equilibrium constant (K) is the value of Q when the reaction is at equilibrium. When Q < K, it indicates that the reaction will proceed in the forward direction to reach equilibrium, favoring the formation of products.
Recommended video:
Guided course
00:49Reaction Quotient Q
Free Energy Diagram
A free energy diagram visually represents the change in Gibbs Free Energy as a reaction progresses from reactants to products. It typically shows the energy levels of reactants and products, along with transition states, and helps identify points of interest, such as where Q is less than K, indicating the direction in which the reaction will favorably proceed.
Recommended video:
Guided course
01:57Energy Diagrams
Related Practice
Textbook Question
Consider the following endothermic reaction of gaseous AB3 molecules with A2 molecules. Identify the true statement about the spontaneity of the reaction. (a) The reaction is likely to be spontaneous at high temperatures. (b) The reaction is likely to be spontaneous at high temperatures. (c) The reaction is always spontaneous.(d) The reaction is always spontaneous.
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Textbook Question
Calculate ∆Stotal, and determine whether the reaction is spon-taneous or nonspontaneous under standard-state conditions. (a) -429 J/K; nonspontaneous (b) -123 J/K; spontaneous (c) +3,530 J/K; nonspontaneous (d) +184 J/K; nonspontaneous
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Textbook Question
Ammonium hydrogen sulfide, a stink bomb ingredient, decomposes to ammonia and hydrogen sulfide: Calculate the standard free-energy change for the rection at 25 °C if the total pressure resulting from the solid NH4S placed in an evacuated container is 0.658 atm at 25 °C.(a) -43.8 kJ(b) +1.04 kJ(c) -462 kJ(d) +5.51 kJ
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Textbook Question
Formation constants for the ammonia and ethylenediamine complexes of nickel(II) indicate that Ni(en)32+ is much more
stable than Ni(NH3)62+:
(1) <REACTION>
(2) <REACTION>
The enthalpy changes for the two reactions, ΔH°1 and ΔH°2, should be about the same because both complexes have six Ni﹣N bonds.
(c) Assuming that ΔH°2 - ΔH°1 is zero, calculate the value of ΔS°2 - ΔS°1.
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Textbook Question
Spinach contains a lot of iron but is not a good source of dietary iron because nearly all the iron is tied up in the oxalate complex [Fe(C2O4)3]3-.
(b) Under the acidic conditions in the stomach, the Fe3+ concentration should be greater because of the reaction
[Fe(C2O4)3]3-(aq) + 6 H3O+(aq) ⇌ Fe3+(aq) + 3 H2C2O4(aq) + 6 H2O(l)
Show, however, that this reaction is nonspontaneous under standard-state conditions. (For H2C2O4, Ka1 = 5.9 × 10-2 and Ka2 = 6.4 × 10-5.)
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