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Ch.16 - Chemical Equilibrium
All textbooksTro 5th EditionCh.16 - Chemical EquilibriumProblem 43
Chapter 16, Problem 43

Consider the reaction: Fe3+ (aq) + SCN- (aq) ⇌ FeSCN2+ (aq). A solution is made containing an initial [Fe3+] of 1.0*10^-3 M and an initial [SCN-] of 8.0*10^-4 M. At equilibrium, [FeSCN2+] = 1.7*10^-4 M. Calculate the value of the equilibrium constant (Kc).

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1
Identify the initial concentrations of the reactants: [Fe^{3+}]_0 = 1.0 \times 10^{-3} \text{ M} and [SCN^-]_0 = 8.0 \times 10^{-4} \text{ M}.
Determine the change in concentration for the formation of FeSCN^{2+} at equilibrium, which is given as [FeSCN^{2+}] = 1.7 \times 10^{-4} \text{ M}.
Calculate the equilibrium concentrations of the reactants: [Fe^{3+}]_{eq} = [Fe^{3+}]_0 - [FeSCN^{2+}] and [SCN^-]_{eq} = [SCN^-]_0 - [FeSCN^{2+}].
Write the expression for the equilibrium constant K_c: K_c = \frac{[FeSCN^{2+}]_{eq}}{[Fe^{3+}]_{eq} \times [SCN^-]_{eq}}.
Substitute the equilibrium concentrations into the K_c expression to find the value of the equilibrium constant.

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 that reactants are favored.
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ICE Table

An ICE table (Initial, Change, Equilibrium) is a tool used to organize the concentrations of reactants and products in a chemical reaction at different stages. It helps in determining the changes in concentration as the reaction progresses towards equilibrium. By filling in the initial concentrations, the changes that occur, and the equilibrium concentrations, one can easily calculate the equilibrium constant.
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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 itself to counteract the change and restore a new equilibrium. This principle is crucial for understanding how changes in concentration, pressure, or temperature can affect the position of equilibrium and the value of the equilibrium constant.
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Related Practice
Textbook Question

Consider the following reaction: H2(g) + I2(g) ⇌ 2 HI(g) Complete the table. Assume that all concentrations are equilibrium concentrations in M.

T (°C) [H2] [I2] [HI] Kc

25 0.0355 0.0388 0.922 _

340 _ 0.0455 0.387 9.6

445 0.0485 0.0468 _ 50.2

Textbook Question

Consider the reaction: 2 NO(g) + Br2(g) ⇌ 2 NOBr(g) Kp = 28.4 at 298K In a reaction mixture at equilibrium, the partial pressure of NO is 108 torr and that of Br2 is 126 torr. What is the partial pressure of NOBr in this mixture?

Textbook Question

Consider the reaction: SO2Cl2(g) ⇌ SO2(g) + Cl2(g) Kp = 2.91⨉103 at 298 K In a reaction at equilibrium, the partial pressure of SO2 is 137 torr and that of Cl2 is 285 torr. What is the partial pressure of SO2Cl2in this mixture?