Calculate the equilibrium concentrations of N2O4 and NO2 at 25 °C in a vessel that contains an initial N2O4 concentration of 0.0500 M. The equilibrium constant Kc for the reaction N2O4(g) ⇌ 2 NO2(g) is 4.64 × 10⁻³ at 25 °C.

Name: Chemistry
Author: McMurry
ISBN: 9781292336145

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Step 1: Write the balanced chemical equation for the reaction: \( \text{N}_2\text{O}_4(g) \rightleftharpoons 2 \text{NO}_2(g) \).

Step 2: Set up an ICE (Initial, Change, Equilibrium) table to track the concentrations of \( \text{N}_2\text{O}_4 \) and \( \text{NO}_2 \) at each stage. Initially, \( [\text{N}_2\text{O}_4] = 0.0500 \text{ M} \) and \( [\text{NO}_2] = 0 \text{ M} \).

Step 3: Define the change in concentration for \( \text{N}_2\text{O}_4 \) as \( -x \) and for \( \text{NO}_2 \) as \( +2x \), where \( x \) is the amount of \( \text{N}_2\text{O}_4 \) that dissociates.

Step 4: Express the equilibrium concentrations in terms of \( x \): \( [\text{N}_2\text{O}_4] = 0.0500 - x \) and \( [\text{NO}_2] = 2x \).

Step 5: Substitute these expressions into the equilibrium constant expression \( K_c = \frac{[\text{NO}_2]^2}{[\text{N}_2\text{O}_4]} \) and solve for \( x \) to find the equilibrium concentrations.

주요 개념

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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 concentration. Understanding this concept is crucial for calculating equilibrium concentrations.

Equilibrium Constant (Kc)

The equilibrium constant (Kc) is a numerical value that expresses the ratio of the concentrations of products to reactants at equilibrium, each raised to the power of their coefficients in the balanced equation. For the reaction N2O4(g) ⇌ 2 NO2(g), Kc = [NO2]² / [N2O4]. This constant provides insight into the position of equilibrium and is essential for calculating the concentrations at equilibrium.

ICE Table

An ICE table (Initial, Change, Equilibrium) is a tool used to organize the concentrations of reactants and products at different stages of a chemical reaction. It helps in tracking the initial concentrations, the changes that occur as the system reaches equilibrium, and the final equilibrium concentrations. Using an ICE table is a systematic approach to solving equilibrium problems, making it easier to visualize and calculate the necessary values.