Reaction Rates (College Board AP® Chemistry)

Exam Questions

41 mins17 questions
11 mark

In a first-order reaction, the half-life of the reactant is 30 minutes. How long will it take for the concentration of the reactant to decrease to 12.5% of its initial value?

  • 60 minutes

  • 90 minutes

  • 120 minutes

  • 150 minutes

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21 mark

Which of the following statements about the integrated rate law for a first-order reaction is true?

  • The x-intercept of the ln[A] vs. t plot represents the half-life of the reaction.

  • The y-intercept of the ln[A] vs. t plot represents the initial concentration of A.

  • The slope of the ln[A] vs. t plot is equal to the rate constant k.

  • The area under the ln[A] vs. t plot represents the total amount of product formed.

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31 mark

The rate expression for the reaction between iodine and propanone is determined to be:

Rate = k [H+] [C3H6O]

Which graph is consistent with this information?

A graph showing four posible lines for the reaction between iodine and propanone

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    4
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    1 mark

    For the reaction

    C2H5Br (aq) + OH- (aq) → C2H5OH (aq) + Br - (aq)

    the following data were collected at constant temperature:

    [C2H5Br] / M

    [OH-] / M

    Rate / M s-1

    3.0 x 10-3

    2.0 x 10-2

    4.0 x 10-4

    6.0 x 10-3

    2.0 x 10-2

    8.0 x 10-4

    6.0 x 10-3

    4.0 x 10-2

    1.6 x 10-3

    What is the correct rate law for this reaction?

    • Rate = k [C2H5Br] [OH-]

    • Rate = k [C2H5Br] [OH-]2

    • Rate = k [C2H5Br]2 [OH-]

    • Rate = k [C2H5Br]2 [OH-]2

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    5
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    1 mark

    2N2O5 (g) → 4NO2 (g) + O2 (g)

    At high temperatures, N2O5 (g) decomposes according to the equation above. A sample of N2O5 (g) is monitored as it decomposes, and the concentration of N2O5 (g) as a function of time is recorded. The results are shown in the table below.

    Time / s

    [N2O5] / M

    0

    0.850

    60.0

    0.654

    120.0

    0.532

    180.0

    0.448

    What is the average rate of the reaction between 120.0 and 180.0 seconds?

    • 7.0 x 10-4 M s-1

    • 1.0 x 10-3 M s-1

    • 1.4 x 10-3 M s-1

    • 1.6 x 10-3 M s-1

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    61 mark

    CaCO3 (g) + H2SO4 (aq) → CaSO4 (aq) + H2O (l) + CO2 (g)

    The reaction between CaCO3 (s) and H2SO4 (aq) is represented by the equation above.

    In a kinetics experiment, a 0.25 g sample of powdered CaCO3 (s) is added to a flask containing 50 mL of 1.5 M H2SO4 (aq) at 25 oC. The rate of the reaction is determined by measuring the volume of CO2 (g) produced over time.

    Which of the following experimental changes is most likely to increase the rate of CO2 (g) production?

    • Using a 0.25 g sample of CaCO3 (s) chips instead of powdered CaCO3 (s).

    • Using 1.0 M H2SO4 (aq) instead of 1.5 M.

    • Using 100 mL of 1.5 M H2SO4 (aq) instead of 50 mL.

    • Warming the H2SO4 (aq) to 35 oC before its addition to the CaCO3 (s).

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    7
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    1 mark

    An investigation into the rate of reaction between compounds A and B was performed. 

    A + B → C + D 

    The results from three different experiments carried out at a constant temperature were collected:

    [A] / M

    [B] / M

    Rate / M s-1

    0.30

    0.50

    6.0 x 10-4

    0.30

    0.25

    1.5 x 10-4

    0.60

    0.25

    3.0 x 10-4

    The rate equation for this reaction is rate = k [A] [B]2

    What is the value of the rate constant, k

    • 4.0 x 10-3

    • 3.2 x 10-2

    • 8.0 x 10-3

    • 2.7 x 10-2

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    8
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    1 mark

    Ammonia decomposes into nitrogen gas and hydrogen gas, at high temperatures. A sample of ammonia is monitored as it decomposes, and the concentration of hydrogen is recorded over time. The results are shown in the table below.

    Time / s

    [H2] / M

    0

    0.646

    60.0

    0.491

    120.0

    0.388

    180.0

    0.318

    What is the average rate of the reaction between 60.0 and 120.0 seconds?

    • 8.5 x 10-4 M s-1

    • 5.7 x 10-4 M s-1

    • 1.7 x 10-3 M s-1

    • 5.2 x 10-3 M s-1

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    91 mark

    A rate law is found to be

    Rate = k [A]2 [B]

    Which of the following changes will not alter the initial rate of reaction?

    • Doubling the concentration of A and B

    • Doubling the concentration of A and halving the concentration of B

    • Halving the concentration of A and doubling the concentration of B

    • Halving the concentration of A and quadrupling the concentration of B

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    10
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    1 mark

    A first-order reaction has a half-life of 62 s. What fraction of reactant remains after 124 s?

    • 1/2

    • 1/4

    • 1/8

    • 1/16

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    111 mark

    For the general reaction V + W + X → Y + Z, the rate equation is: 

    rate = k [V] [W] [X]

    What will happen to the rate of reaction when the concentration of all three reactants is doubled?

    • Increase by a factor of 2

    • Increase by a factor of 4

    • Increase by a factor of 6

    • Increase by a factor of 8

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