Textbook Question
Consider the reaction 3 CH4(g) → C3H8(g) + 2 H2(g). (a) Using data from Appendix C, calculate ΔG° at 298 K.
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Ch.19 - Chemical Thermodynamics
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232
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Table of contents
- Ch.1 - Introduction: Matter, Energy, and Measurement140
- Ch.2 - Atoms, Molecules, and Ions192
- Ch.3 - Chemical Reactions and Reaction Stoichiometry172
- Ch.4 - Reactions in Aqueous Solution156
- Ch.5 - Thermochemistry151
- Ch.6 - Electronic Structure of Atoms137
- Ch.7 - Periodic Properties of the Elements127
- Ch.8 - Basic Concepts of Chemical Bonding143
- Ch.9 - Molecular Geometry and Bonding Theories167
- Ch.10 - Gases147
- Ch.11 - Liquids and Intermolecular Forces97
- Ch.12 - Solids and Modern Materials129
- Ch.13 - Properties of Solutions126
- Ch.14 - Chemical Kinetics175
- Ch.15 - Chemical Equilibrium107
- Ch.16 - Acid-Base Equilibria127
- Ch.17 - Additional Aspects of Aqueous Equilibria133
- Ch.18 - Chemistry of the Environment88
- Ch.19 - Chemical Thermodynamics140
- Ch.20 - Electrochemistry137
- Ch.21 - Nuclear Chemistry99
- Ch.22 - Chemistry of the Nonmetals66
- Ch.23 - Transition Metals and Coordination Chemistry69
- Ch.24 - The Chemistry of Life: Organic and Biological Chemistry11
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Not the one you use?Change textbook
Chapter 19, Problem 75
Indicate whether ΔG increases, decreases, or stays the same for each of the following reactions as the partial pressure of O2 is increased: (a) 2 CO(g) + O2(g) → 2 CO2(g) (b) 2 H2O2(l) → 2 H2O(l) + O2(g) (c) 2 KClO3(s) → 2 KCl(s) + 3 O2(g)
Verified step by step guidance1
Step 1: Understand the relationship between Gibbs free energy change (ΔG) and reaction quotient (Q). The equation ΔG = ΔG° + RT ln(Q) shows that ΔG depends on the reaction quotient Q, which is affected by the partial pressures of gases involved in the reaction.
Step 2: For reaction (a) 2 CO(g) + O₂(g) → 2 CO₂(g), increasing the partial pressure of O₂ will decrease Q because O₂ is a reactant. Since Q decreases, ln(Q) becomes more negative, which decreases ΔG, making the reaction more spontaneous.
Step 3: For reaction (b) 2 H₂O₂(l) → 2 H₂O(l) + O₂(g), increasing the partial pressure of O₂ will increase Q because O₂ is a product. Since Q increases, ln(Q) becomes more positive, which increases ΔG, making the reaction less spontaneous.
Step 4: For reaction (c) 2 KClO₃(s) → 2 KCl(s) + 3 O₂(g), increasing the partial pressure of O₂ will increase Q because O₂ is a product. Since Q increases, ln(Q) becomes more positive, which increases ΔG, making the reaction less spontaneous.
Step 5: Summarize the effects: (a) ΔG decreases, (b) ΔG increases, (c) ΔG increases, as the partial pressure of O₂ is increased.
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Gibbs Free Energy (ΔG)
Gibbs Free Energy (ΔG) is a thermodynamic potential that measures the maximum reversible work obtainable from a thermodynamic system at constant temperature and pressure. It indicates the spontaneity of a reaction: a negative ΔG suggests a spontaneous process, while a positive ΔG indicates non-spontaneity. Understanding how ΔG changes with varying conditions, such as concentration or pressure, is crucial for predicting reaction behavior.
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01:51
Gibbs Free Energy of Reactions
Le Chatelier's Principle
Le Chatelier's Principle states that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium shifts to counteract the change. In the context of gas reactions, increasing the partial pressure of a reactant (like O2) will shift the equilibrium towards the products if the reaction produces fewer moles of gas, thereby affecting the ΔG of the reaction.
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07:32Le Chatelier's Principle
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) describes the ratio at equilibrium. Changes in partial pressures can alter Q, and when Q is compared to K, it helps determine the direction in which the reaction will shift, thus influencing ΔG. Understanding these concepts is essential for analyzing how changes in conditions affect reaction spontaneity.
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Related Practice
Textbook Question
The fuel in high-efficiency natural-gas vehicles consists primarily of methane (CH4). (a) How much heat is produced in burning 1 mol of CH4(g) under standard conditions if reactants and products are brought to 298 K and H2O(l) is formed?
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Textbook Question
Consider the reaction 2 NO2(g) → N2O4(g). (a) Using data from Appendix C, calculate ΔG° at 298 K. (b) Calculate ΔG at 298 K if the partial pressures of NO2 and N2O4 are 0.40 atm and 1.60 atm, respectively.
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Textbook Question
(a) Using data in Appendix C, estimate the temperature at which the free-energy change for the transformation from I2(s) to I2(g) is zero. (b) Use a reference source, such as Web Elements (www.webelements.com), to find the experimental melting and boiling points of I2. (c) Which of the values in part (b) is closer to the value you obtained in part (a)?
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