Chemical Equilibrium and Rate Concepts
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Questions and Answers

What is the overall order of the reaction given the rate law Rate=k[Br-][BrO3-][H+]2?

  • 4 (correct)
  • 2
  • 1
  • 3
  • In the rate law Rate=k[Br-][BrO3-][H+]2, which species is second order?

  • Rate
  • BrO3-
  • H+ (correct)
  • Br-
  • What does the zero-order rate law indicate about the rate of reaction?

  • The rate increases with concentration.
  • The rate is dependent on the temperature only.
  • The rate decreases with time.
  • The rate is constant regardless of concentration. (correct)
  • Which mathematical relationship connects reactant concentration to time for a zero-order reaction?

    <p>[A]t = [A]0 - kt</p> Signup and view all the answers

    How can one transform a rate law into a mathematical relationship between concentration and time?

    <p>By using integration.</p> Signup and view all the answers

    What is the relationship between the concentration of a reactant and the time during a zero-order reaction?

    <p>Independent of the concentration.</p> Signup and view all the answers

    If a reaction has a rate law Rate=k[A]^2[B], what can be inferred about its order with respect to A?

    <p>Second order.</p> Signup and view all the answers

    In the context of reaction kinetics, what is the purpose of an integrated rate law?

    <p>To predict how concentration changes over time.</p> Signup and view all the answers

    What does the average rate of decomposition of N2O5 represent?

    <p>The change in concentration of N2O5 over a time interval</p> Signup and view all the answers

    How is the rate constant 'k' in a rate law described?

    <p>It represents the proportionality constant in the rate reaction</p> Signup and view all the answers

    What happens to the rate of a reaction if the concentration of a reactant increases?

    <p>The rate increases, depending on the reaction order</p> Signup and view all the answers

    In a rate law, what do the exponents associated with each reactant's concentration represent?

    <p>The reaction order with respect to that reactant</p> Signup and view all the answers

    Why can the reaction order not be determined simply by examining the balanced equation?

    <p>It requires experimental determination</p> Signup and view all the answers

    How does the concentration of water affect reaction rates in beakers with the same reactants?

    <p>Higher water concentration results in lower concentrations of reactants</p> Signup and view all the answers

    What defines the change in concentration in the average rate of a reaction?

    <p>Final concentration minus initial concentration</p> Signup and view all the answers

    Which of the following is true about a catalyst's impact on reaction rates?

    <p>It can alter the rate constant of the reaction</p> Signup and view all the answers

    What does the ratio [A]t/[A]0 represent in the context of first-order reactions?

    <p>The fraction of reactant A remaining at time t.</p> Signup and view all the answers

    In a first-order reaction, what is the significance of the rate constant k?

    <p>It is a temperature-dependent constant that influences reaction speed.</p> Signup and view all the answers

    Which of the following statements is true regarding the decomposition of N2O5?

    <p>It is a first-order reaction.</p> Signup and view all the answers

    To find the concentration of a reactant after a specific time in a first-order reaction, which equation would you use?

    <p>ln[A]t = ln[A]0 - kt</p> Signup and view all the answers

    How long would it take for the concentration of N2O5 to decrease to 1.00 × 10-2 mol/L from 1.65 × 10-2 mol/L?

    <p>Approximately 1000 seconds</p> Signup and view all the answers

    What does [A]t indicate in the second-order integrated rate law?

    <p>The concentration of A at a specified time t.</p> Signup and view all the answers

    Which of the following is not part of the first-order rate law?

    <p>Rate of product formation.</p> Signup and view all the answers

    In a first-order reaction, which factor is not directly related to the rate of reaction?

    <p>Product concentration.</p> Signup and view all the answers

    What is indicated by a large equilibrium constant (Keq >> 1) for a reaction?

    <p>The forward reaction is favored, leading to more products than reactants.</p> Signup and view all the answers

    How is the equilibrium constant expression for a reaction constructed?

    <p>By multiplying the concentrations of products, dividing by the concentrations of reactants, and using stoichiometric coefficients as exponents.</p> Signup and view all the answers

    In the equilibrium constant expression for the reaction $N_2O_5(g) \rightleftharpoons 4NO_2(g) + O_2(g)$, what is the correct form of the expression?

    <p>Kc = $[NO_2]^4[O_2] / [N_2O_5]^2$</p> Signup and view all the answers

    What is a likely result of a small equilibrium constant (Keq << 1) for a particular reaction?

    <p>The forward reaction produces minimal products compared to reactants.</p> Signup and view all the answers

    When constructing an equilibrium constant expression, what should be done with the coefficients in the chemical equation?

    <p>They are treated as the powers to which the concentrations are raised.</p> Signup and view all the answers

    What happens to a system at equilibrium if a reactant is added?

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

    Which of the following statements is true regarding equilibrium in chemical reactions?

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

    What does the symbol '>>' signify when reading an equilibrium constant?

    <p>That the concentration of products is significantly greater than reactants.</p> Signup and view all the answers

    What is the half-life of a reaction if the rate constant is given as $2.20 \times 10^{-5}/s$?

    <p>8.75 hr</p> Signup and view all the answers

    In a first-order reaction, what happens to the concentration of reactants as the reaction proceeds?

    <p>It decreases due to consumption.</p> Signup and view all the answers

    How can the concentration of N2O5 be calculated after 825 s given its initial concentration is $1.65 × 10^{-2} mol/L$?

    <p>By using the rate constant and the integrated rate law for first-order reactions.</p> Signup and view all the answers

    What characterizes the dynamic equilibrium in a chemical reaction?

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

    If the concentration of N2O5 decreases from its initial value to $1.00 × 10^{-2} mol/L$, what is necessary to find out how long this takes?

    <p>The integral rate law for first-order reactions.</p> Signup and view all the answers

    Which statement about reversible reactions at equilibrium is accurate?

    <p>The system shows no changes in properties.</p> Signup and view all the answers

    What type of kinetic order does the decomposition of SO2Cl2 follow?

    <p>First-order</p> Signup and view all the answers

    How is the concentration of a substance calculated after a certain time in a first-order reaction?

    <p>By employing the first-order kinetic equation.</p> Signup and view all the answers

    Study Notes

    Chemical Equilibrium

    • In a reversible reaction, the products react to give back the original reactants creating a mixture of both at equilibrium.

    The Equilibrium Constant

    • Equilibrium constant (Kc or Keq) is the value obtained for the equilibrium-constant expression when equilibrium concentrations are substituted.
    • The constant is determined by multiplying the concentrations of products, dividing by concentrations of reactants, and raising each to the power of its coefficient in the balanced chemical equation.
    • For a large equilibrium constant (Keq >> 1), the forward reaction is largely favored and there will be more products than reactants at equilibrium.
    • For small equilibrium constant (Keq << 1), the reverse reaction is largely favored and there will be more reactants than products at equilibrium.

    Precise Definition of Rate

    • Average reaction rate is the change in concentration of a reactant or product over a time interval.
    • The time interval used to calculate the reaction rate is important for determining the average reaction rate.

    Dependence of Rate on Concentration

    • Rate law explains the relationship between the rate of a reaction and the concentrations of reactants.
    • Rate law is determined experimentally and can not be obtained simply by looking at the balanced equation.
    • k is the rate constant, a proportionality constant in the relationship between rate and concentrations.
    • m, n, and p are frequently, but not always, integers and they must be determined experimentally.

    Reaction Order

    • The reaction order with respect to a given reactant species equals the exponent of the concentration of that species in the rate law.
    • The overall order of a reaction equals the sum of the orders of the reactant species in the rate law.

    Change of Concentration with Time

    • An integrated rate law is a mathematical relationship showing how a reactant concentration changes over a period of time.
    • For a zero-order reaction, the rate of the reaction does not change with concentration.
    • The integrated rate law equation for a first-order reaction shows that the concentration of the reactant decreases exponentially with time.
    • The integrated rate law equation for a second-order reaction shows that the concentration of the reactant decreases more rapidly at the beginning of the reaction than at later times.

    Half-Life of a Reaction

    • Half-life (t1/2) is the time it takes for the reactant concentration to decrease to one-half of its initial value.
    • The half-life of a first-order reaction is independent of the initial concentration of the reactant.

    Dynamic Equilibrium

    • Chemical equilibrium is the condition in which the rate of the forward reaction equals the rate of the reverse reaction.
    • This condition is dynamic because the forward and reverse reactions are still occurring but at the same constant rate.

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    Chemistry Lecture 4 PDF

    Description

    This quiz covers the principles of chemical equilibrium and the concept of the equilibrium constant. It explores how reversible reactions reach equilibrium and how to define reaction rates. Dive into the fundamentals of chemical reactions and understand the dynamics of product and reactant concentrations.

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