Textbook Question
b. What are the units of specific heat?
Ch.5 - Thermochemistry
Brown15th EditionChemistry: The Central ScienceISBN: 9780137542970
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Table of contents
- Ch.1 - Introduction: Matter, Energy, and Measurement146
- Ch.2 - Atoms, Molecules, and Ions200
- Ch.3 - Chemical Reactions and Reaction Stoichiometry176
- Ch.4 - Reactions in Aqueous Solution155
- Ch.5 - Thermochemistry126
- Ch.6 - Electronic Structure of Atoms131
- Ch.7 - Periodic Properties of the Elements126
- Ch.8 - Basic Concepts of Chemical Bonding123
- Ch.9 - Molecular Geometry and Bonding Theories143
- Ch.10 - Gases147
- Ch.11 - Liquids and Intermolecular Forces91
- Ch.12 - Solids and Modern Materials122
- Ch.13 - Properties of Solutions126
- Ch.14 - Chemical Kinetics174
- Ch.15 - Chemical Equilibrium101
- Ch.16 - Acid-Base Equilibria139
- Ch.17 - Additional Aspects of Aqueous Equilibria146
- Ch.18 - Chemistry of the Environment72
- Ch.19 - Chemical Thermodynamics129
- Ch.20 - Electrochemistry142
- Ch.21 - Nuclear Chemistry101
- Ch.22 - Chemistry of the Nonmetals68
- Ch.23 - Transition Metals and Coordination Chemistry66
- Ch.24 - The Chemistry of Life: Organic and Biological Chemistry10
Brown15th EditionChemistry: The Central ScienceISBN: 9780137542970Not the one you use?Change textbook
Chapter 5, Problem 48c
Consider the decomposition of liquid benzene, C6H6(l), to gaseous acetylene, C2H2(g): C6H6(l) → 3 C2H2(g) ΔH = +630 kJ (c) Which is more likely to be thermodynamically favored, the forward reaction or the reverse reaction?
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Identify the sign of the enthalpy change (ΔH) for the reaction. A positive ΔH indicates that the reaction is endothermic, meaning it absorbs heat from the surroundings.
Understand that thermodynamically favored reactions are generally those that release energy (exothermic reactions), where ΔH is negative, as they lead to a decrease in the system's enthalpy, making the products more stable than the reactants.
Compare the enthalpy change of the forward reaction, which is +630 kJ, indicating that it is endothermic and requires energy input to proceed.
Consider the reverse reaction, where the sign of ΔH would be negative (-630 kJ), suggesting that it is exothermic. This reaction would release energy, making it more likely to occur spontaneously under standard conditions.
Conclude that the reverse reaction, forming liquid benzene from gaseous acetylene, is more likely to be thermodynamically favored due to its exothermic nature.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Thermodynamics and Reaction Favorability
Thermodynamics is the study of energy transformations, particularly how energy changes influence the direction of chemical reactions. A reaction is thermodynamically favored if it leads to a decrease in free energy, typically indicated by a negative change in Gibbs free energy (ΔG). In this context, the forward reaction's positive enthalpy change (ΔH = +630 kJ) suggests it absorbs heat, which may affect its favorability.
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First Law of Thermodynamics
Enthalpy and Reaction Energy
Enthalpy (H) is a measure of the total energy of a thermodynamic system, including internal energy and the energy required to make room for it by displacing its environment. A positive ΔH indicates that the reaction is endothermic, meaning it requires energy input. Understanding the enthalpy change helps predict whether a reaction will proceed spontaneously under given conditions.
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Entropy and Disorder
Entropy (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, which can favor the reaction despite a positive enthalpy change. In this case, the decomposition of liquid benzene into gaseous acetylene increases the number of gas molecules, potentially making the forward reaction more favorable from an entropy perspective.
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Related Practice
Textbook Question
Consider the decomposition of liquid benzene, C6H6(l), to gaseous acetylene, C2H2(g): C6H6(l) → 3 C2H2(g) ΔH = +630 kJ (a) What is the enthalpy change for the reverse reaction?
Textbook Question
Consider the decomposition of liquid benzene, C6H6(l), to gaseous acetylene, C2H2(g): C6H6(l) → 3 C2H2(g) ΔH = +630 kJ (b) What is H for the formation of 1 mol of acetylene?
Textbook Question
Two solid objects, A and B, are placed in boiling water and allowed to come to the temperature of the water. Each is then lifted out and placed in separate beakers containing 1000 g of water at 10.0 °C. Object A increases the water temperature by 3.50 °C; B increases the water temperature by 2.60 °C. (a) Which object has the larger heat capacity?
Textbook Question
Consider the combustion of isopropanol, C3H7OH(l), which is the primary component of rubbing alcohol: C3H7OH(l) + 9/2 O2(g) → 3 CO2(g) + 4 H2O(l) ΔH = -2248 kJ (b) Balance the forward reaction with whole-number coefficients. What is ΔH for the reaction represented by this equation?
Textbook Question
Consider the decomposition of liquid benzene, C6H6(l), to gaseous acetylene, C2H2(g): C6H6(l) → 3 C2H2(g) ΔH = +630 kJ (d) If C6H6(g) were consumed instead of C6H6(l), would you expect the magnitude of ΔH to increase, decrease, or stay the same? Explain.