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Ch.15 - Chemical Equilibrium
Chapter 15, Problem 24b

Consider the following equilibrium: 2 H2(g) + S2(g) ⇌ 2 H2S(g) Kc = 1.08 × 107 at 700°C (b) Does the equilibrium mixture contain mostly H2 and S2 or mostly H2S?

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Understand the equilibrium expression: The equilibrium constant (Kc) is given for the reaction 2 H2(g) + S2(g) ⇌ 2 H2S(g). It is a measure of the ratio of the concentration of products to reactants at equilibrium.
Write the expression for Kc: The equilibrium constant expression for the reaction is Kc = [H2S]^2 / ([H2]^2 * [S2]).
Analyze the value of Kc: The given Kc value is 1.08 × 10^7, which is a very large number. This indicates that at equilibrium, the concentration of the products (H2S) is much greater than the concentration of the reactants (H2 and S2).
Interpret the equilibrium position: Since Kc is significantly greater than 1, the equilibrium position is heavily shifted towards the products, meaning the equilibrium mixture contains mostly H2S.
Conclude the analysis: Based on the large Kc value, the equilibrium mixture will predominantly consist of H2S rather than H2 and S2.

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Key Concepts

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

Chemical Equilibrium

Chemical equilibrium occurs when the rates of the forward and reverse reactions are equal, resulting in constant concentrations of reactants and products. In this state, the system is dynamic, meaning that reactions continue to occur, but there is no net change in the concentrations. Understanding this concept is crucial for analyzing how changes in conditions affect the position of equilibrium.
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Equilibrium Constant (K<sub>c</sub>)

The equilibrium constant, K<sub>c</sub>, quantifies the ratio of the concentrations of products to reactants at equilibrium, raised to the power of their stoichiometric coefficients. A large K<sub>c</sub> value, such as 1.08 × 10<sup>7</sup>, indicates that at equilibrium, the concentration of products is much greater than that of reactants, suggesting that the reaction favors the formation of products.
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Le Chatelier's Principle

Le Chatelier's Principle states that if a system at equilibrium is subjected to a change in concentration, temperature, or pressure, the system will adjust to counteract that change and restore a new equilibrium. This principle helps predict how the equilibrium position will shift in response to changes, such as adding or removing reactants or products.
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