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Ch.15 - Chemical Equilibrium
All textbooksMcMurry 8th EditionCh.15 - Chemical EquilibriumProblem 134
Chapter 15, Problem 134

For the reaction A2 + 2B ∆ 2 AB, the rate of the for- ward reaction is 18 M/s and the rate of the reverse reaction is 12 M/s. The reaction is not at equilibrium. Will the reaction pro- ceed in the forward or reverse direction to attain equilibrium?

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Identify the rates of the forward and reverse reactions. The rate of the forward reaction is given as 18 M/s, and the rate of the reverse reaction is 12 M/s.
Understand that at equilibrium, the rate of the forward reaction equals the rate of the reverse reaction.
Compare the given rates: since the rate of the forward reaction (18 M/s) is greater than the rate of the reverse reaction (12 M/s), the reaction system is producing AB faster than it is being converted back to A2 and B.
Determine the direction needed to reach equilibrium: To achieve equilibrium, the system needs to slow down the forward reaction or speed up the reverse reaction until both rates are equal.
Conclude that the reaction will proceed in the forward direction to increase the concentration of products (AB), which will eventually increase the rate of the reverse reaction and help attain equilibrium.

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Key Concepts

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

Reaction Rates

Reaction rates refer to the speed at which reactants are converted into products in a chemical reaction. In this case, the forward reaction rate is 18 M/s, while the reverse reaction rate is 12 M/s. Understanding these rates is crucial for determining the direction in which the reaction will proceed to reach equilibrium.
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Average Rate of Reaction

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 scenario, since the forward reaction rate (18 M/s) is greater than the reverse reaction rate (12 M/s), the system is not at equilibrium and will shift towards the formation of more products to achieve balance.
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Thermal Equilibrium

Le Chatelier's Principle

Le Chatelier's Principle states that if a system at equilibrium is disturbed, it will adjust to counteract the disturbance and restore a new equilibrium. In this case, since the forward reaction is faster, the system will favor the forward direction to increase the concentration of products (AB) until the rates of both reactions equalize.
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Related Practice
Textbook Question
Baking soda (sodium bicarbonate) decomposes when it is heated: 2 NaHCO31s2 ∆ Na2CO31s2 + CO21g2 + H2O1g2 ΔH° = + 136 kJ Consider an equilibrium mixture of reactants and products in a closed container. How does the number of moles of CO2 change when the mixture is disturbed by the following: (b) Adding water vapor
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Textbook Question
A platinum catalyst is used in automobile catalytic convert- ers to hasten the oxidation of carbon monoxide: 2 CO1g2 + O 1g2 ∆Pt 2 CO 1g2 ΔH° = - 566 kJ Suppose that you have a reaction vessel containing an equilibrium mixture of CO1g2, O21g2, and CO21g2. Under the following conditions, will the amount of CO increase, decrease, or remain the same? (e) The pressure is increased by adding O2 gas.
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Open Question
Consider the following gas-phase reaction: 2 Ag + Bg ⇌ Cg + Dg. An equilibrium mixture of reactants and products is subjected to the following changes: (a) A decrease in volume (b) An increase in temperature (c) Addition of reactants (d) Addition of a catalyst (e) Addition of an inert gas. Which of these changes affect the composition of the equilibrium mixture but leave the value of the equilibrium constant Kc unchanged? Which of the changes affect the value of Kc? Which affect neither the composition of the equilibrium mixture nor Kc?
Textbook Question
Consider a general, single-step reaction of the type A + B ∆ C. Show that the equilibrium constant is equal to the ratio of the rate constants for the forward and reverse reactions, Kc = kf>kr.
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Textbook Question
Which of the following relative values of kf and kr results in an equilibrium mixture that contains large amounts of reactants and small amounts of products? (a) kf 7 kr (b) kf = kr (c) kf 6 kr
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Textbook Question
Consider the reaction of chloromethane with OH- in aque- ous solution: CH Cl1aq2 + OH-1aq2 ∆kf CH OH1aq2 + Cl-1aq2 At 25 °C, the rate constant for the forward reaction is 6 * 10-6 M-1 s-1, and the equilibrium constant Kc is 1 * 1016. Calculate the rate constant for the reverse reac- tion at 25 °C.
380
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