Chemical Equilibrium and Shifts Quiz
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Questions and Answers

If a catalyst is added to the N2(g) + 3H2(g) ⇌ 2NH3(g) system at equilibrium, what will happen?

  • The equilibrium will not shift, as the catalyst does not affect the equilibrium position. (correct)
  • The equilibrium will shift to the left, decreasing the concentration of NH3.
  • The equilibrium constant, Kc, will increase.
  • The equilibrium will shift to the right, increasing the concentration of NH3.
  • If the total pressure of the N2(g) + 3H2(g) ⇌ 2NH3(g) system is increased by adding an inert gas, such as helium, what will happen to the equilibrium?

  • The equilibrium will not shift, as the inert gas does not participate in the reaction. (correct)
  • The equilibrium constant, Kc, will increase.
  • The equilibrium will shift to the right, increasing the concentration of NH3.
  • The equilibrium will shift to the left, decreasing the concentration of NH3.
  • If the temperature of the N2(g) + 3H2(g) ⇌ 2NH3(g) system is increased, what will happen to the equilibrium constant, Kc?

  • Kc will not change, as the temperature change does not affect the equilibrium constant.
  • Kc will increase, as the reverse reaction is endothermic.
  • Kc will increase, as the forward reaction is endothermic. (correct)
  • Kc will decrease, as the forward reaction is endothermic.
  • If the temperature of the N2(g) + 3H2(g) ⇌ 2NH3(g) system is decreased, what will happen to the equilibrium?

    <p>The equilibrium will shift to the left, decreasing the concentration of NH3.</p> Signup and view all the answers

    According to Le Châtelier's principle, if the pressure of the N2(g) + 3H2(g) ⇌ 2NH3(g) system is increased, what will happen?

    <p>The equilibrium will shift to favor the forward reaction, increasing the concentration of NH3.</p> Signup and view all the answers

    What happens to an equilibrium reaction when an external stress is applied, according to Le Châtelier's principle?

    <p>The equilibrium reaction reverses direction to partially offset the stress</p> Signup and view all the answers

    If the initial concentrations of the N2(g) + 3H2(g) ⇌ 2NH3(g) system are not at equilibrium, and a catalyst is added, what will happen?

    <p>The equilibrium will be reached more quickly, but the final equilibrium composition will not change.</p> Signup and view all the answers

    Which factor does not affect the equilibrium constant Kc in a chemical reaction?

    <p>Catalyst</p> Signup and view all the answers

    In the system involving cis-stilbene and trans-stilbene, if more cis-stilbene is added at equilibrium, what will happen to the concentrations of both compounds?

    <p>Concentration of cis-stilbene increases; concentration of trans-stilbene decreases</p> Signup and view all the answers

    What does Kc = 24.0 at 200 °C represent in the context of a chemical equilibrium reaction?

    <p>Equilibrium constant</p> Signup and view all the answers

    If the concentration of cis-stilbene is initially 0.5 mol/L instead of 1.0 mol/L in the system, how would this change affect the equilibrium concentrations of both cis- and trans-stilbene?

    <p>Concentration of cis-stilbene increases; concentration of trans-stilbene decreases</p> Signup and view all the answers

    How does a change in volume affect a system at equilibrium, based on Le Châtelier's principle?

    <p>Decreasing volume shifts the equilibrium towards the side with more gas molecules</p> Signup and view all the answers

    What is the effect of adding iron(III) nitrate [Fe(NO3)3] to the original solution containing the FeSCN^{2+} equilibrium?

    <p>The red color deepens as the equilibrium shifts to the left.</p> Signup and view all the answers

    How does the addition of oxalic acid (H2C2O4) affect the original red solution containing the FeSCN^{2+} equilibrium?

    <p>The red solution turns yellow due to the formation of Fe(C2O4)3^{3-}.</p> Signup and view all the answers

    According to Le Châtelier's principle, how does an increase in pressure affect the equilibrium of a gaseous reaction?

    <p>The equilibrium shifts towards the side with fewer moles of gas.</p> Signup and view all the answers

    Which of the following relationships correctly describes the ideal gas law?

    <p>All of the above</p> Signup and view all the answers

    According to Le Châtelier's principle, how do changes in pressure affect the concentrations of species in condensed phases (liquids and solids)?

    <p>Concentrations are not affected because liquids and solids are virtually incompressible.</p> Signup and view all the answers

    In the expression $P = \frac{nRT}{V}$, what does the variable C represent?

    <p>Concentration</p> Signup and view all the answers

    Study Notes

    Equilibrium System

    • Increasing pressure in a system decreases volume, resulting in an increase in concentration (n/V) of both reactants and products.
    • This increase in pressure causes Qc > Kc, leading to a shift in the reaction to the left until Qc = Kc.
    • An increase in pressure (decrease in volume) favors the net reaction that decreases the total number of moles of gases.
    • A decrease in pressure (increase in volume) favors the net reaction that increases the total number of moles of gases.

    Le Châtelier's Principle: Changes in Temperature

    • A change in temperature can alter the equilibrium constant.
    • If the forward reaction is endothermic (absorbs heat, ΔH° > 0), an increase in temperature will favor the endothermic direction, resulting in a decrease in [N2O4] and an increase in [NO2].
    • If the forward reaction is exothermic (releases heat, ΔH° < 0), a decrease in temperature will favor the exothermic direction, resulting in a decrease in [NO2] and an increase in [N2O4].
    • The equilibrium constant Kc increases when the system is heated and decreases when the system is cooled.

    Le Châtelier's Principle: The Effect of a Catalyst

    • A catalyst enhances the rate of a reaction by lowering the reaction's activation energy.
    • The presence of a catalyst does not alter the equilibrium constant or shift the position of an equilibrium system.
    • Adding a catalyst to a reaction mixture that is not at equilibrium will cause the mixture to reach equilibrium sooner.

    Factors That Affect Chemical Equilibrium

    • Concentration
    • Pressure
    • Volume
    • Temperature
    • Catalyst (does not change K)

    Le Châtelier's Principle: Changes in Concentration

    • If an external stress is applied to a system at equilibrium, the system adjusts in such a way that the stress is partially offset as the system reaches a new equilibrium position.
    • Examples of concentration changes:
      • Adding sodium thiocyanate (NaSCN) to a solution of iron(III) thiocyanate [Fe(SCN)3] increases the concentration of SCN-, causing the equilibrium to shift from right to left.
      • Adding iron(III) nitrate [Fe(NO3)3] to the original solution increases the concentration of Fe3+, causing the equilibrium to shift from right to left.
      • Adding oxalic acid (H2C2O4) to the original solution decreases the concentration of Fe3+, causing the equilibrium to shift from left to right.

    Le Châtelier's Principle: Changes in Volume and Pressure

    • Changes in pressure generally do not affect the concentrations of species in condensed phases.
    • Gases are compressible and are affected by changes in pressure.
    • The ideal gas law (PV = nRT) can be used to describe the behavior of gases in response to changes in pressure.

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    Description

    Test your knowledge on chemical equilibrium and how the addition of different substances can affect the equilibrium shift. Questions cover the reactions of Fe3+ ions with SCN— ions, as well as the impact of adding iron(III) nitrate [Fe(NO3)3] and oxalic acid (H2C2O4) to a solution.

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