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Ch.15 - Chemical Equilibrium
Chapter 15, Problem 54

At 218Β°C, 𝐾𝑐 = 1.2Γ—10βˆ’4 for the equilibrium NH4SH(𝑠) β‡Œ NH3(𝑔) + H2S(𝑔) Calculate the equilibrium concentrations of NH3 and H2S if a sample of solid NH4SH is placed in a closed vessel at 218Β°C and decomposes until equilibrium is reached.

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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. For the reaction NHβ‚„SH(s) β‡Œ NH₃(g) + Hβ‚‚S(g), Kc = [NH₃][Hβ‚‚S] / [NHβ‚„SH]. Since NHβ‚„SH is a solid, its concentration does not appear in the expression, simplifying the calculation of equilibrium concentrations.
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Le Chatelier's Principle

Le Chatelier's Principle states that if a system at equilibrium is disturbed by changing the conditions (such as concentration, temperature, or pressure), the system will adjust to counteract the disturbance and restore a new equilibrium. In this case, the decomposition of solid NHβ‚„SH into gaseous products will shift the equilibrium position to favor the formation of NH₃ and Hβ‚‚S until the equilibrium concentrations are established.
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Stoichiometry of the Reaction

Stoichiometry involves the quantitative relationships between the reactants and products in a chemical reaction. For the decomposition of NHβ‚„SH, the stoichiometry indicates that one mole of NHβ‚„SH produces one mole of NH₃ and one mole of Hβ‚‚S. This relationship is crucial for calculating the equilibrium concentrations of the gaseous products based on the initial amount of solid NHβ‚„SH and the value of Kc.
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Related Practice
Textbook Question

At 2000Β°C, the equilibrium constant for the reaction 2 NO(𝑔) β‡Œ N2(𝑔) + O2(𝑔) is 𝐾𝑐 = 2.4Γ—103. If the initial concentration of NO is 0.175 M, what are the equilibrium concentrations of NO, N2, and O2?

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Textbook Question

For the equilibrium Br2(𝑔) + Cl2(𝑔) β‡Œ 2 BrCl(𝑔) at 400 K, 𝐾𝑐 = 7.0. If 0.25 mol of Br2 and 0.55 mol of Cl2 are introduced into a 3.0-L container at 400 K, what will be the equilibrium concentrations of Br2, Cl2, and BrCl?

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Textbook Question

At 373 K, 𝐾𝑝 = 0.416 for the equilibrium 2 NOBr(𝑔) β‡Œ 2 NO(𝑔) + Br2(𝑔) If the pressures of NOBr(𝑔) and NO(𝑔) are equal, what is the equilibrium pressure of Br2(𝑔)?

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Textbook Question

At 80Β°C, 𝐾𝑐 = 1.87Γ—10βˆ’3 for the reaction PH3BCl3(𝑠) β‡Œ PH3(𝑔) + BCl3(𝑔) (a) Calculate the equilibrium concentrations of PH3 and BCl3 if a solid sample of PH3BCl3 is placed in a closed vessel at 80Β°C and decomposes until equilibrium is reached.

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Textbook Question

At 80Β°C, 𝐾𝑐 = 1.87Γ—10βˆ’3 for the reaction PH3BCl3(𝑠) β‡Œ PH3(𝑔) + BCl3(𝑔) (a) Calculate the equilibrium concentrations of PH3 and BCl3 if a solid sample of PH3BCl3 is placed in a closed vessel at 80Β°C and decomposes until equilibrium is reached. (b) If the flask has a volume of 0.250 L, what is the minimum mass of PH3BCl3(𝑠) that must be added to the flask to achieve equilibrium?

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Textbook Question

At 25Β°C, the reaction CaCrO4(𝑠) β‡Œ Ca2+(π‘Žπ‘ž) + CrO42βˆ’(π‘Žπ‘ž) has an equilibrium constant 𝐾𝑐 = 7.1Γ—10βˆ’4. What are the equilibrium concentrations of Ca2+ and CrO42βˆ’ in a saturated solution of CaCrO4?

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