Introduction to Chemical Equilibrium
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Questions and Answers

What does the term 'chemical equilibrium' refer to?

  • The complete conversion of reactants to products.
  • The state where the concentrations of reactants and products remain constant over time. (correct)
  • The highest energy state of a reaction system.
  • The condition in which the forward reaction stops occurring.

    • Which statement is true regarding the equilibrium constant K?

  • K remains constant at a specific temperature for a given reaction. (correct)
  • K can equal 0 under certain conditions.
  • K changes with temperature for a given reaction.
  • K is variable and depends on the concentration of reactants only.

    • What is the impact of the presence of pure solids and liquids on the position of a chemical equilibrium?

  • They alter the concentrations of reactants and products.
  • They do not affect the position of chemical equilibrium. (correct)
  • They significantly shift the equilibrium position.
  • They are included in the equilibrium constant expression.

    • In which of the following scenarios would you NOT expect the equilibrium constant K to remain constant?

    <p>Changing the temperature of the reaction.</p> Signup and view all the answers

    What is the primary purpose of equilibrium constant expressions?

    <p>To describe the concentration relationships at equilibrium.</p> Signup and view all the answers

    What does the activity coefficient, γx, represent in the context of chemical equilibria?

    <p>It measures the effectiveness of a species in influencing an equilibrium.</p> Signup and view all the answers

    How does the activity coefficient of a species vary with ionic strength in moderately concentrated solutions?

    <p>It is independent of the specific electrolyte present.</p> Signup and view all the answers

    What happens to the activity coefficient as the solution approaches infinite dilution?

    <p>It equals the molar concentration, [X].</p> Signup and view all the answers

    Which of the following statements about the activity coefficient and ionic strength is correct?

    <p>The relationship of activity coefficient with ionic strength is not linear.</p> Signup and view all the answers

    What is the relationship between activity (ax) and molar concentration ([X]) in a solution?

    <p>ax is the product of γx and [X].</p> Signup and view all the answers

    To calculate the activity coefficient for Hg21 in a solution with an ionic strength of 0.085 M, what is necessary aside from ionic strength?

    <p>The effective diameter of the ion.</p> Signup and view all the answers

    Which of the following factors does NOT affect the activity coefficient in moderately concentrated solutions?

    <p>Nature of the electrolyte.</p> Signup and view all the answers

    In the context of chemical equilibrium, what is the role of electrolytes?

    <p>They influence the concentrations of reactants and products.</p> Signup and view all the answers

    What is the effective diameter used for calculating the activity coefficient for Hg2+ in a solution?

    <p>0.5 nm</p> Signup and view all the answers

    What ionic strength is used in the calculation of the activity coefficient for Hg2+?

    <p>0.085 M</p> Signup and view all the answers

    Which of the following is NOT one of the three types of algebraic equations used in solving multiple-equilibrium problems?

    <p>Rate Expression</p> Signup and view all the answers

    In the context of the equilibrium-constant expression, which substances are typically NOT included?

    <p>Solids and liquids</p> Signup and view all the answers

    Which expression relates the concentration ratio of products to reactants in a chemical reaction?

    <p>Equilibrium Constant Expression</p> Signup and view all the answers

    What calculation is required to determine the activity coefficient specifically for Hg2+?

    <p>Use of Equation 10-5</p> Signup and view all the answers

    Which of the following statements is true regarding the properties of activity coefficients?

    <p>Activity coefficients are influenced by ionic strength.</p> Signup and view all the answers

    What is the primary purpose of a charge balance expression in multiple-equilibrium problems?

    <p>To ensure the total charge is conserved</p> Signup and view all the answers

    What is the relationship between K and Kp in chemical equilibrium?

    <p>Kp is based on partial pressures, while K is based on molar concentrations.</p> Signup and view all the answers

    How does the ionic strength of a solution affect chemical equilibria?

    <p>It affects equilibria independent of the electrolyte's chemical nature.</p> Signup and view all the answers

    For a strong electrolyte solution containing only singly charged ions, how does ionic strength compare to total molar salt concentration?

    <p>Ionic strength is equal to the molar concentration.</p> Signup and view all the answers

    Which of the following statements about the effect of ions with multiple charges on ionic strength is correct?

    <p>Ionic strength increases more than molar concentration with multicharged ions.</p> Signup and view all the answers

    When predicting the direction of a reaction towards equilibrium, which factor is primarily examined?

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

    What does a high value of Kc indicate about a chemical reaction at equilibrium?

    <p>The products are favored over the reactants.</p> Signup and view all the answers

    In which scenario would the reaction quotient (Q) be equal to the equilibrium constant (K)?

    <p>When the reaction has reached equilibrium.</p> Signup and view all the answers

    What implies that a system is not at equilibrium?

    <p>Q is significantly different from K in either direction.</p> Signup and view all the answers

    What does the mass balance expression for a 0.20 M H3AsO4 account for?

    <p>[H3AsO4] + [H2AsO4- ] + [HAsO42-] + [AsO43-]</p> Signup and view all the answers

    In a solution where the charge balance equation is [Na+] + [H3O+] = [OH-] + [H2AsO4-] + 2[HAsO42-] + 3[AsO43-], what does [Na+] represent?

    <p>The concentration of sodium cations</p> Signup and view all the answers

    What is the analytical concentration, CX, of a solute?

    <p>The moles of solute in 1 L of solution</p> Signup and view all the answers

    Which mass balance expression is correct for a 0.10 M Na2HAsO4?

    <p>0.10 = [H3AsO4] + [H2AsO4- ] + [HAsO42-] + [AsO43-]</p> Signup and view all the answers

    Why is charge balance important in electrolyte solutions?

    <p>The positive and negative charges must be equal for neutrality.</p> Signup and view all the answers

    What would be the result if the mass balance equation for H3AsO4 is incorrectly stated?

    <p>It will lead to an incorrect interpretation of species concentrations.</p> Signup and view all the answers

    For a 0.20 M H3AsO4 solution, which conclusion can be drawn about the equilibrium concentrations?

    <p>The sum of molar concentrations must equal 0.20 M.</p> Signup and view all the answers

    Which of the following indicates a weak acid in the context of mass-balance equations?

    <p>A reversible reaction with partial ionization.</p> Signup and view all the answers

    Study Notes

    Introduction to Chemical Equilibrium

    • Chemical Equilibrium occurs when the rate of the forward reaction equals the rate of the reverse reaction.
    • The Law of Mass Action states that the equilibrium constant (K) is constant for a given reaction at equilibrium and a constant temperature.
    • The equilibrium constant (K) for a reaction can be a value for K for equilibrium concentrations (Keq) or equilibrium pressures (Kp).
    • Equilibrium constants do not depend on the amount of pure solids or liquids present, as their concentrations remain constant.
    • The relationship between Keq and Kp is dependent on the change in the number of moles of gas (Δn) in a reaction: Kp = Keq(RT)Δn.

    Solubility Product Constants

    • Solubility product constants (Ksp) are used to describe the solubility of sparingly soluble ionic compounds.
    • The lower the Ksp value, the lower the solubility of the salt.
    • Ksp values are calculated using the concentrations of the ions present at equilibrium, assuming that the solid salt does not contribute significantly to the total concentration of ions in the solution.

    Effects of Electrolytes on Chemical Equilibrium

    • The effect of added electrolytes on equilibria is independent of the electrolyte's nature but dependent on the solution's ionic strength.

    Ionic Strength

    • Ionic strength (μ) is defined as: μ=1/2∑(Zi2[Ci]).
    • The ionic strength of a solution containing singly charged ions is equal to the total molar salt concentration.
    • The ionic strength is higher than the molar concentration if the solution contains ions with multiple charges.

    Activity Coefficients

    • Activity (ax ) is defined as the effective concentration of a species that influences an equilibrium.
    • Activity coefficients (γx) are dimensionless factors representing the effectiveness of a species.
    • Activity coefficients are independent of the electrolyte's nature and dependent on ionic strength at low concentrations.

    Solving Multiple-Equilibrium Problems

    • Multiple-equilibrium problems can be solved by using a systematic method that employs three types of algebraic equations:
    • Equilibrium Constant Expressions: describe the concentration ratios of reactants and products at equilibrium.
    • Mass Balance Expressions: relate the equilibrium concentrations of various species in a solution to their analytical concentrations.
    • Charge Balance Expressions: ensure electrical neutrality in the solution by equating the sum of positive charges to the sum of negative charges.

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    Description

    This quiz covers the fundamentals of chemical equilibrium, including the Law of Mass Action and the calculation of equilibrium constants. It also explores solubility product constants and their significance in determining the solubility of ionic compounds. Test your understanding of these key concepts in chemistry.

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