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Ch.15 - Chemical Equilibrium
McMurry - Chemistry 8th Edition
McMurry8th EditionChemistryISBN: 9781292336145Not the one you use?Change textbook
All textbooksMcMurry 8th EditionCh.15 - Chemical EquilibriumProblem 15.65
Chapter 15, Problem 15.65

Calculate the value of the equilibrium constant for the reaction 4 NH31g2 + 3 O21g2 ∆ 2 N21g2 + 6 H2O1g2
given the following equilibrium constants at a certain temperature.
2 H21g2 + O21g2 ∆ 2 H2O1g2 Kc = 3.2 * 1081
N21g2 + 3 H21g2 ∆ 2 NH31g2 Kc = 3.5 * 108

Verified step by step guidance
1
Identify the given reactions and their equilibrium constants. The first reaction is 2 H2(g) + O2(g) ⇌ 2 H2O(g) with Kc = 3.2 * 10^8, and the second reaction is N2(g) + 3 H2(g) ⇌ 2 NH3(g) with Kc = 3.5 * 10^8.
Write the target reaction: 4 NH3(g) + 3 O2(g) ⇌ 2 N2(g) + 6 H2O(g).
Break down the target reaction into reactions that involve the given equilibrium constants. This can be done by reversing the second given reaction and multiplying it by 2, and using the first given reaction multiplied by 3.
Calculate the equilibrium constant for the reversed reaction of NH3 formation by taking the reciprocal of the given Kc for that reaction, since reversing a reaction inverts its equilibrium constant (Kc' = 1/Kc).
Combine the equilibrium constants of the adjusted reactions using the rule that when reactions are added, their equilibrium constants are multiplied. For the reversed reaction, use the reciprocal value calculated in the previous step.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Equilibrium Constant (Kc)

The equilibrium constant (Kc) 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. It is calculated using the formula Kc = [products]^[coefficients] / [reactants]^[coefficients]. A larger Kc indicates a greater concentration of products at equilibrium, while a smaller Kc suggests a higher concentration of reactants.
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Reaction Stoichiometry

Reaction stoichiometry refers to the quantitative relationships between the reactants and products in a chemical reaction, as represented by their coefficients in the balanced equation. Understanding stoichiometry is essential for manipulating equilibrium constants, as it allows for the adjustment of the reaction's coefficients to derive the equilibrium constant for a different reaction based on known constants.
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Le Chatelier's Principle

Le Chatelier's Principle states that if a dynamic equilibrium is disturbed by changing the conditions, the system will adjust to counteract the change and restore a new equilibrium. This principle is crucial when considering how changes in concentration, pressure, or temperature can affect the position of equilibrium and, consequently, the value of the equilibrium constant.
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Related Practice
Textbook Question

If Kc = 7.5×10−9 at 1000 K for the reaction N2(g) + O2(g) → 2 NO(g), give the value of Kc at 1000 K for the reaction

(a) 2 NO(g) → N2(g) + O2(g)

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Textbook Question

Calculate the value of the equilibrium constant at 427 °C for the reaction

Na O1s2 + 1>2 O 1g2 ∆ Na O 1s2

given the following equilibrium constants at 427 °C.

Na2O1s2 ∆ 2 Na1l2 + 1>2 O21g2 Kc = 2 * 10-25 Na O 1s2 ∆ 2 Na1l2 + O 1g2 K = 5 * 10-29

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Textbook Question

If Kc = 7.5×10−9 at 1000 K for the reaction N2(g) + O2(g) → 2 NO(g), give the value of Kc at 1000 K for the reaction

(b) NO(g) → 1/2 N2(g) + 1/2 O2(g)

89
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Textbook Question

The reaction

2 PH31g2 + As21g2 ∆ 2 AsH31g2 + P21g2

has Kp = 2.9 * 10-5 at 873 K. At the same temperature,

what is Kp for each of the following reactions?

(a) 2 AsH31g2 + P21g2 ∆ 2 PH31g2 + As21g2

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