Textbook Question
An equilibrium mixture of N2, H2, and NH3 at 700 K con- tains 0.036 M N2 and 0.15 M H2. At this temperature, Kc for the reaction N21g2 + 3 H21g2 ∆ 2 NH31g2 is 0.29. What is the concentration of NH3?
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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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04:21
Chemical Equilibrium Concepts
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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01:14Equilibrium Constant K
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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02:10Concentration Changes and Rate Law Example
Related Practice
Open Question
An equilibrium mixture of O2, SO2, and SO3 contains equal concentrations of SO2 and SO3. Calculate the concentration of O2 if Kc = 2.7 * 10^2 for the reaction 2 SO2(g) + O2(g) ⇌ 2 SO3(g).
Open Question
The air pollutant NO is produced in automobile engines from the high-temperature reaction N2(g) + O2(g) ⇌ 2 NO(g); Kc = 1.7 * 10^-3 at 2300 K. If the initial concentrations of N2 and O2 at 2300 K are both 1.40 M, what are the concentrations of NO, N2, and O2 when the reaction mixture reaches equilibrium?
Open Question
The interconversion of l-___-lysine and l-b-lysine, for which Kc = 7.20 at 333 K, is catalyzed by the enzyme lysine 2,3-aminomutase. Lysine occurs in proteins while l-b-lysine is a precursor to certain antibiotics. At 333 K, a solution of l-___-lysine at a concentration of 3.00 * 10^-3 M is placed in contact with lysine 2,3-aminomutase. What are the equilibrium concentrations of l-___-lysine and l-b-lysine?
Textbook Question
The value of Kc for the reaction of acetic acid with ethanol is 3.4 at 25°C:
CH3CO2H1soln2 + CH3CH2OH1soln2 ∆
Acetic acid Ethanol CH3CO2CH2CH31soln2 + H2O1soln2 Kc = 3.4 (a) How many moles of ethyl acetate are present in an equi- librium mixture that contains 4.0 mol of acetic acid,
6.0 mol of ethanol, and 12.0 mol of water at 25 °C?
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Open Question
In a basic aqueous solution, chloromethane undergoes a substitution reaction in which Cl- is replaced by OH-: CH3Cl(aq) + OH-(aq) ⇌ CH3OH(aq) + Cl-(aq). The equilibrium constant Kc is 1 * 10^16. Calculate the equilibrium concentrations of CH3Cl, CH3OH, OH-, and Cl- in a solution prepared by mixing equal volumes of 0.1 M CH3Cl and 0.2 M NaOH. (Hint: In defining x, assume that the reaction goes 100% to completion, and then take account of a small amount of the reverse reaction.)