Textbook Question
Which of the following reactions has ∆Ssys> 0?(a) N2(g) + 3H2(g) -> 2NH3(g)(b) Ag+(aq) + Cl-(aq) -> AgCl(s)(c) 2H2O2(aq) -> 2H2O(l) + O2(g)(d) 2I(g) -> I2(g)
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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 & Measurement170
- Ch.2 - Atoms, Molecules & Ions160
- Ch.3 - Mass Relationships in Chemical Reactions169
- Ch.4 - Reactions in Aqueous Solution199
- Ch.5 - Periodicity & Electronic Structure of Atoms102
- Ch.6 - Ionic Compounds: Periodic Trends and Bonding Theory92
- Ch.7 - Covalent Bonding and Electron-Dot Structures61
- Ch.8 - Covalent Compounds: Bonding Theories and Molecular Structure59
- Ch.9 - Thermochemistry: Chemical Energy122
- Ch.10 - Gases: Their Properties & Behavior155
- Ch.11 - Liquids & Phase Changes54
- Ch.12 - Solids and Solid-State Materials73
- Ch.13 - Solutions & Their Properties120
- Ch.14 - Chemical Kinetics98
- Ch.15 - Chemical Equilibrium125
- Ch.16 - Aqueous Equilibria: Acids & Bases110
- Ch.17 - Applications of Aqueous Equilibria147
- Ch.18 - Thermodynamics: Entropy, Free Energy & Equilibrium86
- Ch.19 - Electrochemistry154
- Ch.20 - Nuclear Chemistry96
- Ch.21 - Transition Elements and Coordination Chemistry156
- Ch.22 - The Main Group Elements187
- Ch.23 - Organic and Biological Chemistry51
Chapter 18, Problem 7
Identify the true statement about a spontaneous process. (a) A reaction that is nonspontaneous in the forward direction is spontaneous in the reverse direction.(b) Adding a catalyst will cause a nonspontaneous reaction to become spontaneous.(c) In a spontaneous process, the entropy of the system always decreases.(d) An endothermic reaction is always spontaneous.
Verified step by step guidance1
Step 1: Understand the concept of spontaneity. A spontaneous process is one that occurs without needing to be driven by an external force.
Step 2: Analyze option (a). A reaction that is nonspontaneous in the forward direction is indeed spontaneous in the reverse direction, according to the second law of thermodynamics.
Step 3: Evaluate option (b). Adding a catalyst does not change the spontaneity of a reaction; it only speeds up the rate at which equilibrium is reached.
Step 4: Consider option (c). In a spontaneous process, the total entropy of the system and surroundings increases, but the entropy of the system itself can decrease.
Step 5: Review option (d). An endothermic reaction is not always spontaneous; spontaneity depends on both enthalpy and entropy changes, as described by the Gibbs free energy equation: \( \Delta G = \Delta H - T\Delta S \).
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Spontaneity of Reactions
A spontaneous process is one that occurs without external intervention, typically characterized by a decrease in free energy. Spontaneity is determined by the Gibbs free energy change (ΔG); if ΔG is negative, the process is spontaneous. This concept is crucial for understanding how reactions proceed in nature and the conditions under which they occur.
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Spontaneity of Processes
Entropy and the Second Law of Thermodynamics
Entropy is a measure of disorder or randomness in a system, and the Second Law of Thermodynamics states that the total entropy of an isolated system can never decrease over time. In spontaneous processes, the total entropy of the universe (system plus surroundings) increases, which often drives reactions forward. Understanding entropy helps clarify why some reactions are spontaneous while others are not.
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Role of Catalysts
Catalysts are substances that increase the rate of a chemical reaction without being consumed in the process. They work by lowering the activation energy required for the reaction to occur. However, catalysts do not change the spontaneity of a reaction; they cannot make a nonspontaneous reaction spontaneous, as they do not affect the overall energy change of the reaction.
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Related Practice
Textbook Question
What is the change in entropy (∆S) when 1.32 g of propane (C3H8) at 0.100 atm pressure is compressed by a factor of five at a constant temperature at 20°C? Assume that propane behaves as an ideal gas. (a) ∆S = +13 J/K(b) ∆S = -13 J/K (c) ∆S = - 0.40 J/K(d) ∆S = + 0.40 J/K
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Textbook Question
Magnesium m#etal has ΔHfusion = 9.037 kJ>mol and ΔSfusion = 9.79 J>1K mol2. What is the melting point of magnesium in °C? (LO 11.4)(a) 0.923 °C (b) 923 °C(c) 650 °C (d) 1.08 * 103 °C
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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
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
Nitrogen reacts with fluorine to form nitrogen trifluoride: Calculate ∆G°, and determine whether the equilibrium composition should favor reactions or products at 25 °C(a) ∆G° = -6.7 kJ; the equilibrium composition should favor products. (b) ∆G° = -332 kJ; the equilibrium composition should favor reactants (c) ∆G° = -166 kJ; the equilibrium composition should favor products (d) ∆G° = +82.6 kJ; the equilbirum composiiton should favor reactants.
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