Chemical Equilibrium Concepts
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Questions and Answers

What happens to the equilibrium when a reaction component is added?

  • Equilibrium remains unchanged with respect to concentrations.
  • Equilibrium shifts to produce more of that component.
  • Equilibrium constant increases due to the addition.
  • Equilibrium shifts to consume some of the added component. (correct)

    • How does an increase in volume affect equilibrium when gases are involved?

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

    • What is true about temperature increases in endothermic reactions?

  • Equilibrium shifts towards the products. (correct)
  • Equilibrium shifts towards the reactants.
  • The equilibrium constant remains unchanged.
  • The reaction rate decreases.

    • How do catalysts affect the rate of reactions at equilibrium?

    <p>They speed up both forward and reverse reactions equally.</p> Signup and view all the answers

    What happens to the equilibrium constant when the temperature of an exothermic reaction is increased?

    <p>It decreases, favoring the reactants.</p> Signup and view all the answers

    What characterizes a system at chemical equilibrium?

    <p>The rates of the forward and reverse reactions are equal.</p> Signup and view all the answers

    Which statement is true regarding the equilibrium constant (K)?

    <p>It is the same for all reactions at a given temperature.</p> Signup and view all the answers

    In the given reaction N2O4 (g) ⇌ 2NO2 (g), what does the double arrow signify?

    <p>Both forward and reverse reactions are occurring.</p> Signup and view all the answers

    At equilibrium, what remains constant?

    <p>The amounts of reactants and products.</p> Signup and view all the answers

    Which expression correctly represents the equilibrium constant K for the reaction N2O4 (g) ⇌ 2NO2 (g)?

    <p>$K = \frac{NO2^2}{N2O4}$</p> Signup and view all the answers

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

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

    How can you define equilibrium in a chemical system?

    <p>The rates of formation of products and reactants are equal.</p> Signup and view all the answers

    Which of the following best represents the relationship between the forward and reverse reaction rates at equilibrium?

    <p>Rate of forward reaction = Rate of reverse reaction.</p> Signup and view all the answers

    What is the expression for the equilibrium constant Kc for the reaction N2(g) + 3H2(g) ⇌ 2NH3(g)?

    <p>$\frac{[NH_3]^2}{[N_2][H_2]^3}$</p> Signup and view all the answers

    In Experiment 1, what is the equilibrium concentration of N2O4?

    <p>0.0172 M</p> Signup and view all the answers

    Which experiment shows the same value of Kc as Experiment 2?

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

    What initial concentration of NO2 leads to the highest equilibrium concentration of N2O4 in the experiments provided?

    <p>0.0200 M</p> Signup and view all the answers

    Why does the equilibrium constant Kc depend on concentrations at equilibrium?

    <p>It indicates the position of equilibrium.</p> Signup and view all the answers

    What Kc value corresponds to the initial concentration of NO2 at 0.0400 M in Experiment 3?

    <p>0.213</p> Signup and view all the answers

    Which statement about the initial conditions of the experiments is true?

    <p>All experiments started with only N2O4.</p> Signup and view all the answers

    What is the relationship between the change in concentrations and stoichiometry in chemical reactions?

    <p>The changes are proportional to their coefficients in the balanced equation.</p> Signup and view all the answers

    What does a K value significantly greater than 1 indicate about a chemical reaction?

    <p>The products predominantly form at equilibrium.</p> Signup and view all the answers

    In the equation for Kp, what does Dn represent?

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

    Which of the following correctly represents the relationship between Kp and Kc?

    <p>Kp = Kc * R(T)</p> Signup and view all the answers

    If a reaction reaches an equilibrium state, what can be said about the concentrations of the reactants and products?

    <p>The concentrations remain constant over time.</p> Signup and view all the answers

    What is the purpose of calculating equilibrium concentrations?

    <p>To predict the concentrations of substances at equilibrium.</p> Signup and view all the answers

    When performing equilibrium calculations, what is typically used to account for changes in concentrations?

    <p>A factor 'x' based on stoichiometry.</p> Signup and view all the answers

    What happens to the equilibrium position if the concentration of a reactant is increased?

    <p>The equilibrium shifts to favor products.</p> Signup and view all the answers

    In a reaction represented by Kc, what does it mean when Kc = 50.5 at a given temperature?

    <p>The reaction favors products significantly.</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 value when a system at equilibrium is disturbed?

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

    Which value of x is deemed physically meaningful when solving for equilibrium concentrations?

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

    In the equilibrium expression Kc = \[HI^2 / (H_2)(I_2)\], what does HI represent?

    <p>The concentration of the product hydrogen iodide.</p> Signup and view all the answers

    Using the quadratic formula, what is one of the roots calculated from the equation 0.9207x^2 - 3x + 2 = 0?

    <p>2.323</p> Signup and view all the answers

    What is the relationship between the initial concentrations and the changes in concentrations in the equilibrium expression?

    <p>The changes in concentrations do not affect initial concentrations.</p> Signup and view all the answers

    What is the correct expression for the equilibrium constant Kc for the reaction H2 + I2 ⇌ 2HI?

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

    What is the correct equilibrium expression for the generalized reaction aA + bB ⇌ dD + eE?

    <p>$K_c = \frac{[D][E]}{[A][B]}$</p> Signup and view all the answers

    Which statement about Kp and Kc is correct?

    <p>Kp applies only to reactions at equilibrium conditions.</p> Signup and view all the answers

    For the Haber process, what is the expression for Kc?

    <p>$K_c = \frac{[NH3]^2}{[N2][H2]^3}$</p> Signup and view all the answers

    What does it mean if a reaction has reached equilibrium?

    <p>The rates of the forward and reverse reactions are equal.</p> Signup and view all the answers

    Which of the following is NOT true about the equilibrium constant?

    <p>It is dependent on the initial concentrations of reactants.</p> Signup and view all the answers

    In the equilibrium expression for Kp, which of the following represents the correct format?

    <p>$K_p = \frac{(P_D)^d(P_E)^e}{(P_A)^a(P_B)^b}$</p> Signup and view all the answers

    If the concentration of products increases in a reaction at equilibrium, what will happen?

    <p>The equilibrium will shift to produce more reactants.</p> Signup and view all the answers

    Which of the following correctly defines how the equilibrium constant is influenced by temperature?

    <p>It varies with changes in temperature according to the reaction's enthalpy.</p> Signup and view all the answers

    Study Notes

    Chemical Equilibrium

    • Chemical equilibrium occurs when a reaction and its reverse reaction proceed at the same rate.
    • Equilibrium is characterized by constant concentrations of reactants and products.
    • At equilibrium, the rates of the forward and reverse reactions are equal.

    The Equilibrium Constant

    • The equilibrium constant (K) is a ratio of product concentrations to reactant concentrations at equilibrium.

    • For the general reaction aA + bB ⇌ dD + eE, the equilibrium constant expression is: Kc = [D]d[E]e / [A]a[B]b

    • Kp is the equilibrium constant expressed in terms of partial pressures for gaseous reactions. Kp = (PD)d(PE)e / (PA)a(PB)b

    • The magnitude of K indicates the extent of a reaction at equilibrium.

      • K >> 1: Products predominate
      • K << 1: Reactants predominate
      • K ≈ 1: Significant amounts of both reactants and products present

    Haber Process

    • The Haber process is the industrial preparation of ammonia (NH₃).
    • The reaction is: N₂(g) + 3H₂(g) ⇌ 2NH₃(g)
    • The equilibrium constant (Kc) depends on stoichiometry Kc = [NH₃]2 / [N₂][H₂]3

    Achieving Equilibrium

    • Equilibrium is reached regardless of starting conditions (reactants or products).
    • Relative amount of change in concentration is determined by stoichiometry.

    Evaluating K

    • Kc (or Kp) is constant at a specific temperature (for a given reaction).
    • Experiments show equilibrium concentrations are reached regardless of initial concentrations of reactants and products.

    Equilibrium Constants in Terms of Pressure

    • For gases, PV = nRT, or P = [n/V]RT.
    • Consequently, the relationship between Kc and Kp is Kp = Kc(RT)Δn. Where: Δn = (moles of gaseous products) – (moles of gaseous reactants)

    Using Equilibrium Constants

    • If K is greater than 1, the reaction favours products.
    • If K is less than 1, the reaction favours reactants.

    The Direction of the Chemical Equation and K

    • The equilibrium constant for a reaction in the reverse direction is the reciprocal of the equilibrium constant of the forward reaction.

    Relating Stoichiometry and Equilibrium Constants

    • If a reaction's equation is multiplied by a number, simply raise the original equilibrium constant to that power.
    • If a reaction's equation is divided by a number, take the appropriate root of the original equilibrium constant.

    Exam 1, The Review

    • Topics include the Ideal Gas Law, partial pressures, non-ideal gases, intermolecular forces, kinetics, rate laws, order of reactions, and mechanisms

    Combining Equilibrium Expressions

    • When two consecutive equilibria occur, their equations can be combined to yield a single equilibrium.
    • The equilibrium constant of the new reaction is equal to the product of the equilibrium constants of the original reactions.

    Heterogeneous Equilibria

    • In homogeneous equilibria, all reactants and products are in the same phase.
    • In heterogeneous equilibria, at least one component is in a different phase.
    • The concentration of pure solids (s) or liquids (l) is not included in the equilibrium expression.

    Calculating Equilibrium Constants

    • Tabulate initial and equilibrium concentrations.
    • Determine the change in concentrations from initial to equilibrium.
    • Use the balanced equation to find changes for other reactants and products based on stoichiometry.
    • Use the initial concentrations and changes to find equilibrium concentrations for all species.
    • Calculate the equilibrium constant (Kc).

    A Kc Calculation Example

    • Worked example demonstrating the calculation of the equilibrium constant(Kc) for the reaction H2(g) + I2(g) ⇌ 2HI(g).

    The Reaction Quotient, Q

    • Q is the ratio of product concentrations to reactants at any given time, whether equilibrium present or not..
    • Its expression is the same form as Kc or Kp.
    • Q helps determine where the reaction is relative to equilibrium.

    Comparing Q and K

    • If Q < K, the reaction will proceed forward to produce more products.
    • If Q > K, the reaction will proceed backward to produce more reactants.
    • If Q=K, the reaction is at equilibrium.

    Calculating Equilibrium Concentrations

    • If you know the equilibrium constant, you can find the equilibrium concentrations from the initial concentrations, and changes.
    • Set up a table (similar to previous example) but the "change in concentration" row will be a factor(x) of the stoichiometry

    An Equilibrium Calculation: Example

    • Example of an equilibrium calculation showing step-by-step calculations to find equilibrium concentration.

    Le Chatelier's Principle

    • Any disturbance to a system at equilibrium will cause the system to shift to relieve the stress.
    • The equilibrium shift responds to changes in concentration, pressure, and temperature.

    How Conditions Change Equilibrium

    • Explaining effects of concentration, pressure, and temperature.
    • Changes in pressure (and thus volume) favor the side that has fewer moles of gas.
    • Changes in temperature favor the endothermic (heat acting as a reactant) or exothermic (heat acting as a product) side of the reaction.

    Change in Reactant or Product Concentration

    • Adding a reactant or product shifts the equilibrium in the direction that consumes the added component.
    • Removal of a reactant or product shifts the equilibrium to form more of that thing.
    • Equilibrium constant remains the same

    Change in Volume or Pressure

    • In gaseous equilibria, a change in pressure or volume affects the equilibrium with respect to the number of gas molecule's present.

    Change in Temperature

    • Endothermic reactions will favor products as temperature increases, by absorbing heat, this drives the reaction.
    • Exothermic reactions will favor reactants as temperature increases, the extra heat will drive the reaction backwards.
    • Changes in temperature affect the value of the equilibrium constant.

    The Effect of Catalysts

    • Catalysts accelerate the rate of both the forward and reverse reactions.
    • Equilibrium is reached much faster, but the equilibrium composition remains unchanged.
    • Catalysts do not affect the equilibrium constant (K) of the reaction.

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    Chapter 15 Chemical Equilibrium PDF

    Description

    This quiz explores the principles of chemical equilibrium, including the characteristics of equilibrium and the equilibrium constant (K). It covers key concepts, such as the expressions for Kc and Kp, and how to interpret the magnitude of K in different scenarios. Test your knowledge on how reaction dynamics balance at equilibrium.

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