AP®ChemistryCollege BoardExam QuestionsUnit 5: KineticsElementary Reactions & Collisions

Elementary Reactions & Collisions (College Board AP® Chemistry): Exam Questions

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Elementary Reactions & Collisions

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11 mark

For the elementary reaction A + B → C, what is the correct rate law?

  • Rate = k[A][B]

  • Rate = k[A] + k[B]

  • Rate = k[A]2 [B]

  • Rate = k[C] / ([A][B])

Choose your answer

21 mark

According to the collision model, which of the following factors does NOT directly affect the rate of a chemical reaction?

  • Activation energy

  • Enthalpy change of the reaction

  • Frequency of collisions

  • Orientation of colliding molecules

Choose your answer

11 mark

Which of the following statements about reaction mechanisms is true?

  • Catalysts are not involved in elementary reactions.

  • Intermediates appear in the overall balanced equation.

  • The rate-determining step is always the last step in a mechanism.

  • The sum of the elementary steps must equal the overall balanced equation.

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21 mark

How does an increase in temperature affect the Maxwell-Boltzmann distribution of molecular energies?

  • It narrows the distribution and shifts the peak to higher energies.

  • It widens the distribution and shifts the peak to lower energies.

  • It narrows the distribution and shifts the peak to lower energies.

  • It widens the distribution and shifts the peak to higher energies.

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31 mark

How does the average kinetic energy of a gas vary with temperature?

hard-3

    Choose your answer

    11 mark

    The Maxwell-Boltzmann distribution of the distribution of molecular energies in sample 1 of a gas is shown.

    Maxwell-Boltzmann curves for 2 different experiments plooted on the same graph

    A change was made to the reaction conditions, as shown by the dotted curve, labelled sample 2.

    What factor was changed in the reaction conditions to produce the dotted curve, labelled sample 2?

    Temperature increased

    Catalyst added 

    Volume reduced

    A

    X

    X

    ✓

    B

    X

    X

    X

    C

    ✓

    X

    X

    D

    X

    ✓

    X

      Choose your answer

      21 mark

      The Arrhenius equation is given as:

      k equals A e to the power of negative fraction numerator E subscript a over denominator R T end fraction end exponent

      Which of the following best describes the role of the pre-exponential factor (A) in the Arrhenius equation?

      • It represents the fraction of molecules with sufficient energy to react, considering the effect of temperature.

      • It accounts for the total number of molecular collisions and the fraction of correctly oriented collisions that result in a reaction.

      • It is directly proportional to activation energy and determines the minimum energy required for reaction.

      • It is the probability that a molecule will have enough energy to overcome the activation barrier.

      Choose your answer

      31 mark

      The diagrams below show Boltzmann energy distribution curves and activation energy lines for a chemical reaction:

      hard-8

      In Diagram 1, line P or Q represents the activation energy with a catalyst, while the other represents the activation energy without a catalyst.

      In Diagram 2, curve X or Y corresponds to a higher temperature than the other curve.

      Which combination correctly identifies the line and curve?

      Activation Energy with Catalyst

      Higher Temperature

      A

      P

      X

      B

      P

      Y

      C

      Q

      X

      D

      Q

      Y

        Choose your answer