Consider the following equilibrium between oxides of nitrogen 3 NO(g) ⇌ NO₂(g) + N₂O(g) (a) Use data in Appendix C to calculate ΔH° for this reaction.

Name: Chemistry: The Central Science
Author: Brown
ISBN: 9780134414232

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Identify the standard enthalpies of formation (ΔH°f) for each compound involved in the reaction from Appendix C. You will need the values for NO(g), NO₂(g), and N₂O(g).

Write the balanced chemical equation for the reaction: 3 NO(g) ⇌ NO₂(g) + N₂O(g).

Apply the formula for the standard enthalpy change of the reaction (ΔH°rxn): ΔH°rxn = ΣΔH°f(products) - ΣΔH°f(reactants). Remember to multiply the ΔH°f of each substance by its stoichiometric coefficient in the balanced equation.

Calculate the sum of the standard enthalpies of formation for the products: (1 mole of NO₂(g) × ΔH°f of NO₂(g)) + (1 mole of N₂O(g) × ΔH°f of N₂O(g)).

Calculate the sum of the standard enthalpies of formation for the reactants: 3 moles of NO(g) × ΔH°f of NO(g).

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 for the calculation of ΔH° for reactions that may not be easily measured directly by using known enthalpy changes of related reactions.

Standard Enthalpy of Formation (ΔH°f)

The standard enthalpy of formation (ΔH°f) is the change in enthalpy when one mole of a compound is formed from its elements in their standard states. This value is crucial for calculating the enthalpy change of a reaction using Hess's Law, as it provides a reference point for the energy content of reactants and products.

Equilibrium Constant (K)

The equilibrium constant (K) is a numerical value that expresses the ratio of the concentrations of products to reactants at equilibrium for a given reaction at a specific temperature. Understanding K is essential for analyzing the position of equilibrium and how changes in conditions can affect the reaction, which is relevant when considering the enthalpy changes in reactions involving gases.

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Equilibrium Constant K

Related Practice

Textbook Question

Methanol (CH₃OH) can be made by the reaction of CO with H₂: CO(𝑔) + 2 H₂(𝑔) ⇌ CH₃OH(𝑔) (b) To maximize the equilibrium yield of methanol, would you use a high or low temperature?

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Textbook Question

Methanol (CH₃OH) can be made by the reaction of CO with H₂: CO(𝑔) + 2 H₂(𝑔) ⇌ CH₃OH(𝑔) (a) Use thermochemical data in Appendix C to calculate ΔH° for this reaction.

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Textbook Question

Consider the reaction 4 NH₃(𝑔) + 5 O₂(𝑔) ⇌ 4 NO(𝑔) + 6 H₂O(𝑔), Δ𝐻 = −904.4 kJ Does each of the following increase, decrease, or leave unchanged the yield of NO at equilibrium? (f) increase temperature.

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Textbook Question

Consider the following equilibrium between oxides of nitrogen

3 NO(g) ⇌ NO₂(g) + N₂O(g)

(c) At constant temperature, would a change in the volume of the container affect the fraction of products in the equilibrium mixture?

Consider the following equilibrium between oxides of nitrogen 3 NO(g) ⇌ NO2(g) + N2O(g) (a) Use data in Appendix C to calculate ΔH° for this reaction.

Key Concepts

Hess's Law

Standard Enthalpy of Formation (ΔH°f)

Equilibrium Constant (K)

Consider the following equilibrium between oxides of nitrogen 3 NO(g) ⇌ NO₂(g) + N₂O(g) (a) Use data in Appendix C to calculate ΔH° for this reaction.