Textbook Question
Given the data N2(g) + O2(g) → 2 NO(g) ΔH = +180.7 kJ 2 NO(g) + O2(g) → 2 NO2(g) ΔH = -113.1 kJ 2 N2O(g) → 2 N2(g) + O2(g) ΔH = -163.2 kJ use Hess's law to calculate ΔH for the reaction N2O(g) + NO2(g) → 3 NO(g)
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Ch.5 - Thermochemistry
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 5, Problem 63
Calculate the enthalpy change for the reaction P4O6(s) + 2 O2(g) → P4O10(s) given the following enthalpies of reaction: P4(s) + 3 O2(g) → P4O6(s) ΔH = -1640.1 kJ P4(s) + 5 O2(g) → P4O10(s) ΔH = -2940.1 kJ
Verified step by step guidance1
Identify the target reaction: P_4O_6(s) + 2 O_2(g) → P_4O_10(s).
Write the given reactions: 1) P_4(s) + 3 O_2(g) → P_4O_6(s) with ΔH = -1640.1 kJ, 2) P_4(s) + 5 O_2(g) → P_4O_10(s) with ΔH = -2940.1 kJ.
Reverse the first reaction to match the formation of P_4O_6(s) as a reactant: P_4O_6(s) → P_4(s) + 3 O_2(g), changing the sign of ΔH to +1640.1 kJ.
Add the reversed first reaction to the second reaction to cancel out P_4(s) and some O_2(g), resulting in the target reaction.
Calculate the enthalpy change for the target reaction by adding the ΔH values of the modified reactions: ΔH = (+1640.1 kJ) + (-2940.1 kJ).
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Enthalpy of Reaction
Enthalpy of reaction, or ΔH, is the heat change associated with a chemical reaction at constant pressure. It indicates whether a reaction is exothermic (releases heat, ΔH < 0) or endothermic (absorbs heat, ΔH > 0). Understanding the enthalpy changes for specific reactions is crucial for calculating the overall enthalpy change in a multi-step reaction.
Hess's Law
Hess's Law states that the total enthalpy change for a reaction is the sum of the enthalpy changes for the individual steps, regardless of the pathway taken. This principle allows chemists to calculate the enthalpy change for a reaction that may not be easily measured directly by using known enthalpy changes from related reactions.
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Stoichiometry
Stoichiometry involves the calculation of reactants and products in chemical reactions based on balanced chemical equations. It is essential for determining the proportions of substances involved in a reaction, which is necessary when applying Hess's Law to find the overall enthalpy change for a reaction involving multiple steps.
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Related Practice
Textbook Question
(a) Why does the standard enthalpy of formation of both the very reactive fluorine (F2) and the almost inert gas nitrogen (N2) both read zero?
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Textbook Question
Consider the following hypothetical reactions: A → B ΔHI = +60 kJ B → C ΔHII = -90 kJ (a) Use Hess’s law to calculate the enthalpy change for the reaction A → C.
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Textbook Question
From the enthalpies of reaction H2(g) + F2(g) → 2 HF(g) ΔH = -537 kJ C(s) + 2 F2(g) → CF4(g) ΔH = -680 kJ 2 C(s) + 2 H2(g) → C2H4(g) ΔH = +52.3 kJ Calculate H for the reaction of ethylene with F2: C2H4(g) + 6 F2(g) → 2 CF4(g) + 4 HF(g)
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Textbook Question
Under constant-volume conditions, the heat of combustion of naphthalene (C10H8) is 40.18 kJ/g. A 2.50-g sample of naphthalene is burned in a bomb calorimeter. The temperature of the calorimeter increases from 21.50 to 28.83 °C. (c) Suppose that in changing samples, a portion of the water in the calorimeter were lost. In what way, if any, would this change the heat capacity of the calorimeter?
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Textbook Question
Consider the following hypothetical reactions: A → B ΔHI = +60 kJ B → C ΔHII = -90 kJ (b) Construct an enthalpy diagram for substances A, B, and C, and show how Hess's law applies.
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