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Ch.15 - Chemical Equilibrium
Chapter 15, Problem 94

Recalculate the equilibrium concentrations in Problem 15.93 if the initial concentrations are 2.24 M N2 and 0.56 M O2. (This N2>O2 concentration ratio is the ratio found in air.)

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Identify the balanced chemical equation for the reaction involving N2 and O2. For example, if the reaction is N2 + O2 ⇌ 2NO, write it down.
Write the expression for the equilibrium constant (Kc) based on the balanced equation. For the example reaction, Kc = [NO]^2 / ([N2][O2]).
Set up an ICE (Initial, Change, Equilibrium) table to track the concentrations of reactants and products. Start with the initial concentrations: [N2] = 2.24 M, [O2] = 0.56 M, and assume [NO] = 0 M initially.
Define the change in concentration for each species in terms of a variable, usually x. For example, if x is the change in concentration of NO, then the changes for N2 and O2 would be -x/2 and -x/2, respectively, based on stoichiometry.
Substitute the equilibrium concentrations from the ICE table into the Kc expression and solve for x. Use this value to find the equilibrium concentrations of all species.

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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. At equilibrium, the system's composition remains unchanged over time, and the equilibrium constant (K) can be used to express the ratio of product concentrations to reactant concentrations at this state.
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Equilibrium Constant (K)

The equilibrium constant (K) 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 chemical equation. It provides insight into the position of equilibrium; a large K indicates a reaction that favors products, while a small K suggests reactants are favored.
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Initial Concentrations and Changes

In equilibrium problems, the initial concentrations of reactants and products are crucial for determining how the system will shift to reach equilibrium. Changes in concentration, often represented by 'x', are calculated based on the stoichiometry of the reaction, allowing for the determination of equilibrium concentrations by applying the initial values and the changes that occur as the system stabilizes.
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