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AP®ChemistryCollege BoardExam QuestionsUnit 5: KineticsElementary Reactions & Collisions

Elementary Reactions & Collisions (College Board AP® Chemistry)

Exam Questions

8 mins8 questions
Medium
Hard
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

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])

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31 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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41 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

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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

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    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 correctly describe the role of the constant A in the equation?

    I. It accounts for the fraction of collisions with the correct orientation.

    II. It accounts for the energy of the colliding particles.

    III. It accounts for the number of collisions between particles.

    • I and II only

    • I and III only

    • II and III only

    • I, II, and III

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    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

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      41 mark

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

      hard-3

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