Chemical Equilibrium Quiz
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Questions and Answers

What is the effect on equilibrium when a reactant is added to an equilibrium system?

  • Some reactant will be consumed. (correct)
  • Some product will be produced.
  • No change occurs in the equilibrium position.
  • Equilibrium constant will increase.

    • How does an increase in volume affect an equilibrium system involving gases?

  • It favors the side with more moles of gas. (correct)
  • It decreases the equilibrium constant.
  • It favors the side with fewer moles of gas.
  • It has no effect on the equilibrium.

    • What happens to the equilibrium constant K when heat is added to an endothermic reaction?

  • K decreases.
  • Equilibrium cannot be established.
  • K remains unchanged.
  • K increases. (correct)

    • What is the effect of a catalyst on an equilibrium system?

    <p>It increases the rate of reaching equilibrium without changing the composition.</p> Signup and view all the answers

    Which of the following is true when the pressure of a gaseous equilibrium system is increased?

    <p>It has no effect if the number of moles on both sides is equal.</p> Signup and view all the answers

    What is the value of Kc for both experiments 1 and 2?

    <p>0.211</p> Signup and view all the answers

    Which equilibrium concentration of NO2 is observed in experiment 3?

    <p>0.0310 M</p> Signup and view all the answers

    In which experiment does N2O4 have a nonzero initial concentration?

    <p>Experiment 4</p> Signup and view all the answers

    What is the change in concentration of N2O4 from initial to equilibrium in experiment 3?

    <p>0.00448 M</p> Signup and view all the answers

    What is the initial concentration of NO2 in experiment 4?

    <p>0.0 M</p> Signup and view all the answers

    What can be concluded about the Kc values from the experiments?

    <p>Kc remains constant at specific concentrations.</p> Signup and view all the answers

    What is the equilibrium concentration of N2O4 in experiment 2?

    <p>0.00280 M</p> Signup and view all the answers

    How does the stoichiometry of the reaction affect Kc values?

    <p>Kc must be calculated using stoichiometric coefficients.</p> Signup and view all the answers

    What defines the state of chemical equilibrium in a reaction?

    <p>The concentrations of reactants and products remain constant.</p> Signup and view all the answers

    Which equation represents the forward reaction for the given equilibrium?

    <p>N2O4 (g) ® 2 NO2 (g)</p> Signup and view all the answers

    In the expression for the equilibrium constant (K), what do the letters kf and kr represent?

    <p>The rate constants for the forward and reverse reactions, respectively.</p> Signup and view all the answers

    What happens to the rates of the forward and reverse reactions as a system approaches equilibrium?

    <p>Both rates approach equality.</p> Signup and view all the answers

    Which of the following is true regarding the equilibrium constant expression?

    <p>The equilibrium constant changes with temperature.</p> Signup and view all the answers

    At equilibrium, if the concentration of products were to increase, what would happen?

    <p>The rate of the reverse reaction would increase to restore balance.</p> Signup and view all the answers

    What does the double arrow in a chemical equilibrium equation signify?

    <p>The reaction is reversible.</p> Signup and view all the answers

    Which of the following statements best describes the substances at equilibrium?

    <p>Both reactants and products exist at constant concentrations.</p> Signup and view all the answers

    What is the equilibrium concentration of H2 at equilibrium?

    <p>0.065 M</p> Signup and view all the answers

    What happens to the equilibrium constant when the system is disturbed?

    <p>It remains the same.</p> Signup and view all the answers

    If x equals 2.323, what does this value imply in context?

    <p>It leads to a negative concentration for H2.</p> Signup and view all the answers

    Which of the following is the correct expression for the equilibrium constant Kc for the reaction?

    <p>Kc = [HI]^2/([H2][I2])</p> Signup and view all the answers

    How does the concentration of HI change as the system reaches equilibrium?

    <p>It decreases by 2x.</p> Signup and view all the answers

    What is the calculated equilibrium concentration of I2 based on the given value of x?

    <p>1.065 M</p> Signup and view all the answers

    What is the significance of a system's ability to return to equilibrium after disturbance?

    <p>It illustrates the dynamic nature of equilibrium.</p> Signup and view all the answers

    Upon calculating the quadratic equation for x, which of the following values is valid?

    <p>0.935</p> Signup and view all the answers

    What does the equilibrium constant Kc represent in a chemical reaction?

    <p>The ratio of products to reactants at equilibrium in terms of concentration</p> Signup and view all the answers

    In the context of the Haber process, which equation represents Kc?

    <p>Kc = [NH3]^2 / ([N2][H2]^3)</p> Signup and view all the answers

    How does pressure relate to concentration in terms of equilibrium for gases?

    <p>Pressure is proportional to concentration in a closed system.</p> Signup and view all the answers

    What is the correct way to express the equilibrium constant Kp?

    <p>Kp = (PD^d)(PE^e) / (PA^a)(PB^b)</p> Signup and view all the answers

    What can be said about the starting materials in a reaction reaching equilibrium?

    <p>The starting amounts have no effect on the equilibrium state.</p> Signup and view all the answers

    In a generalized reaction aA + bB ⇌ dD + eE, what does the 'a' in the expression Kc signify?

    <p>The stoichiometric coefficient of A in the balance equation</p> Signup and view all the answers

    What is the relationship between Kc and Kp at a given temperature for a gaseous reaction?

    <p>They are related by the expression Kp = Kc(RT)^(Δn)</p> Signup and view all the answers

    What does it indicate if a reaction achieves equilibrium?

    <p>No further change will occur in the concentrations of reactants and products.</p> Signup and view all the answers

    What happens to the ratio of concentrations at equilibrium regardless of initial concentrations of NO2 and N2O4?

    <p>It stays constant at 100°C.</p> Signup and view all the answers

    What is the relationship between Kp and Kc for a reaction involving gases?

    <p>Kp can be calculated using Kc and the change in moles of gases.</p> Signup and view all the answers

    If K is significantly greater than 1, the reaction favors which of the following?

    <p>Products predominating at equilibrium.</p> Signup and view all the answers

    In the context of equilibrium concentration calculation, what role does 'x' play?

    <p>It indicates the change in concentration based on stoichiometry.</p> Signup and view all the answers

    What would be the effect of increasing the concentration of reactants on the value of Kc?

    <p>Kc would remain unchanged.</p> Signup and view all the answers

    If a reaction has Kc = 50.5 at 448 °C, what does this indicate about the equilibrium state?

    <p>The products greatly exceed the reactants at equilibrium.</p> Signup and view all the answers

    What does the variable Dn represent in the relationship between Kp and Kc?

    <p>Difference in moles of gaseous products and reactants.</p> Signup and view all the answers

    When calculating equilibrium concentrations, what type of table is typically set up?

    <p>A stoichiometric change table based on initial concentrations.</p> Signup and view all the answers

    Study Notes

    Chemical Equilibrium

    • Chemical equilibrium is when the forward and reverse reactions proceed at the same rate.
    • Equilibrium is reached when the concentrations of reactants and products no longer change.
    • At equilibrium, the rate of the forward reaction equals the rate of the reverse reaction.

    The Equilibrium Constant (K)

    • The equilibrium constant (K) is a measure of the ratio of products to reactants at equilibrium.
    • For the general reaction aA + bB ⇌ cC + dD, the equilibrium constant expression is Kc = [C]c[D]d / [A]a[B]b
      • where [ ] represents the concentration of the species.
    • Kp is used for gaseous species and is expressed in terms of partial pressures: Kp = (PC)c(PD)d / (PA)a(PB)b
    • K is constant at a given temperature.

    Magnitude of K

    • If K >>1, the reaction strongly favors products at equilibrium.
    • If K <<1, the reaction strongly favors reactants at equilibrium.

    The Reaction Quotient (Q)

    • The reaction quotient (Q) is a measure of the relative amounts of products and reactants at any point in a reaction.
    • Q is calculated using the same expression as K but with the concentrations (or pressures) at any given point in the reaction, not just at equilibrium.
    • If Q < K, the reaction will proceed to form more products to reach equilibrium.
    • If Q = K the mixture is at equilibrium and concentrations are changing no longer.
    • If Q > K, the reaction will proceed towards the reactants to reach equilibrium.

    Calculating Equilibrium Concentrations

    • Tabulate all known initial and equilibrium concentrations.
    • Calculate the change in concentrations using the balanced equation.
    • Use stoichiometry and the known changes to find the equilibrium concentrations of all species.
    • Finally, calculate the equilibrium constant using these equilibrium concentrations.

    Le Chatelier's Principle

    • If a change is applied to a system in dynamic equilibrium, the equilibrium will shift in a way that relieves the stress.
    • Changes in concentration, pressure (volume), or temperature will cause a shift in the equilibrium position.
    • The equilibrium constant will not change.

    Temperature Changes

    • Endothermic Reactions: Heat acts like a reactant. Increasing temperature favours the forward reaction (products), increasing K.
    • Exothermic Reactions: Heat acts like a product. Increasing temperature favour the reverse reaction (reactants) leading to a decrease in K.

    Catalysts

    • Catalysts increase the rate of both the forward and reverse reactions, but they do not shift the equilibrium position.
    • Equilibrium is achieved faster when a catalyst is present.

    Heterogeneous Equilibria

    • Heterogeneous equilibria occur when a reaction involves substances in different phases (solid, liquid, gas).
    • The concentration of pure solids and liquids are not included in the equilibrium constant expression.

    Haber Process

    • The Haber process is the industrial synthesis of ammonia from nitrogen and hydrogen.
    • The stoichiometry and equilibrium constant expression for the reaction.

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    Chapter 15 Chemical Equilibrium PDF

    Description

    Test your knowledge on chemical equilibrium concepts, including the equilibrium constant (K) and its importance in reactions. Understand how the magnitudes of K indicate the favorability of products versus reactants. This quiz covers essential principles from chemistry related to equilibrium.

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