Textbook Question
Write balanced equations that describe the formation of the following compounds from elements in their standard states, and then look up the standard enthalpy of formation for each substance in Appendix C: (a) NH4NO3(s)
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Ch.5 - Thermochemistry
Brown15th EditionChemistry: The Central ScienceISBN: 9780137542970
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Table of contents
- Ch.1 - Introduction: Matter, Energy, and Measurement111
- Ch.2 - Atoms, Molecules, and Ions166
- Ch.3 - Chemical Reactions and Reaction Stoichiometry138
- Ch.4 - Reactions in Aqueous Solution127
- Ch.5 - Thermochemistry104
- Ch.6 - Electronic Structure of Atoms109
- Ch.7 - Periodic Properties of the Elements107
- Ch.8 - Basic Concepts of Chemical Bonding102
- Ch.9 - Molecular Geometry and Bonding Theories120
- Ch.10 - Gases122
- Ch.11 - Liquids and Intermolecular Forces79
- Ch.12 - Solids and Modern Materials102
- Ch.13 - Properties of Solutions99
- Ch.14 - Chemical Kinetics153
- Ch.15 - Chemical Equilibrium83
- Ch.16 - Acid-Base Equilibria109
- Ch.17 - Additional Aspects of Aqueous Equilibria117
- Ch.18 - Chemistry of the Environment60
- Ch.19 - Chemical Thermodynamics109
- Ch.20 - Electrochemistry113
- Ch.21 - Nuclear Chemistry79
- Ch.22 - Chemistry of the Nonmetals52
- Ch.23 - Transition Metals and Coordination Chemistry57
- Ch.24 - The Chemistry of Life: Organic and Biological Chemistry7
Brown15th EditionChemistry: The Central ScienceISBN: 9780137542970Not the one you use?Change textbook
Chapter 5, Problem 66
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)
Verified step by step guidance1
Identify the target reaction: \( \text{N}_2\text{O}(g) + \text{NO}_2(g) \rightarrow 3 \text{NO}(g) \).
Write down the given reactions and their enthalpy changes: \( \text{N}_2(g) + \text{O}_2(g) \rightarrow 2 \text{NO}(g) \), \( \Delta H = +180.7 \text{ kJ} \); \( 2 \text{NO}(g) + \text{O}_2(g) \rightarrow 2 \text{NO}_2(g) \), \( \Delta H = -113.1 \text{ kJ} \); \( 2 \text{N}_2\text{O}(g) \rightarrow 2 \text{N}_2(g) + \text{O}_2(g) \), \( \Delta H = -163.2 \text{ kJ} \).
Reverse the third reaction to match the target reaction's reactants: \( 2 \text{N}_2(g) + \text{O}_2(g) \rightarrow 2 \text{N}_2\text{O}(g) \), changing \( \Delta H \) to \(+163.2 \text{ kJ} \).
Adjust the stoichiometry of the reactions to match the target reaction: Divide the first reaction by 2 to get \( \text{N}_2(g) + \frac{1}{2} \text{O}_2(g) \rightarrow \text{NO}(g) \), and divide the second reaction by 2 to get \( \text{NO}(g) + \frac{1}{2} \text{O}_2(g) \rightarrow \text{NO}_2(g) \).
Combine the adjusted reactions to form the target reaction, ensuring that the intermediates cancel out, and sum the enthalpy changes to find \( \Delta H \) for the target reaction.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Hess's Law
Hess's Law states that the total enthalpy change for a chemical reaction is the sum of the enthalpy changes for the individual steps of the reaction, regardless of the pathway taken. This principle allows chemists to calculate the enthalpy change for a reaction that may be difficult to measure directly by using known enthalpy changes of related reactions.
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Hess's Law
Enthalpy Change (ΔH)
Enthalpy change (ΔH) is a measure of the heat content of a system at constant pressure. It indicates whether a reaction is exothermic (releases heat, ΔH < 0) or endothermic (absorbs heat, ΔH > 0). Understanding ΔH is crucial for predicting the energy changes associated with chemical reactions and for applying Hess's Law effectively.
Stoichiometry
Stoichiometry involves the calculation of reactants and products in chemical reactions based on the balanced chemical equation. It is essential for determining the proportions of substances involved in reactions, which is necessary when applying Hess's Law to combine multiple reactions and find the overall enthalpy change for a target reaction.
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01:16Stoichiometry Concept
Related Practice
Textbook Question
For each of the following compounds, write a balanced thermochemical equation depicting the formation of one mole of the compound from its elements in their standard states and then look up H °f for each substance in Appendix C. (b) FeCl3(s)
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Textbook Question
The concentration of alcohol 1CH3CH2OH2 in blood, called the 'blood alcohol concentration' or BAC, is given in units of grams of alcohol per 100 mL of blood. The legal definition of intoxication, in many states of the United States, is that the BAC is 0.08 or higher. What is the concentration of alcohol, in terms of molarity, in blood if the BAC is 0.08?
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Textbook Question
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
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Textbook Question
Consider the following hypothetical reactions: A → B ΔH = +30 kJ B → C ΔH = +60 kJ (b) Construct an enthalpy diagram for substances A, B, and C, and show how Hess's law applies.
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