A LevelChemistryOCRExam Questions5. Physical Chemistry & Transition Elements (A Level Only)5.1 Rates, Orders & Arrhenius

Rates, Orders & Arrhenius (OCR A Level Chemistry)

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5.1 Rates, Orders & Arrhenius

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5.1 Rates, Orders & Arrhenius

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11 mark

The reaction between iodine and propanone can be catalysed by sulfuric acid. The rate equation shows that this reaction is first order with respect to propanone:

Rate = k [H+] [C3H6O]

Which graph shows that the reaction is first order with respect to propanone?

5-1-q1

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    21 mark

    Substances W and X react in solution according to the equation.

    W + 2X → Y + 2Z

    The results of an investigation of the reaction between W and X are shown in this table.

    Experiment

    Initial [W]
    / mol dm–3

    Initial [X]
    / mol dm–3

    Initial rate
    / mol dm–3 s–1
    1 0.50 0.50 7.0 x 10-4
    2 0.50 1.00 To be calculated

     

    The reaction is zero order with respect to W and first order with respect to X.

    What is the initial rate of experiment 2?

    • 2.8 x 10-3 mol dm–3 s–1

    • 1.4 x 10-3 mol dm–3 s–1

    • 7.0 x 10-4 mol dm–3 s–1

    • 3.5 x 10-4 mol dm–3 s–1

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    31 mark

    The rate equation for the reaction between X and Y is:

    Rate = k [X] [Y]

    What are the correct units for the rate constant, k, of this rate equation?

    • mol dm-3 s-1

    • mol2 dm-6 s-1

    •  dm6 mol-2 s-1

    •  dm3 mol-1 s-1

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    41 mark

    The Arrhenius equation is shown below.

    k = Ae-Ea / RT

    Which term from the Arrhenius equation has the incorrect units?

      Term Units
    A Ea J mol-1
    B R J K-1 mol-1
    C T K
    D e No units

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      51 mark

      An alternative version of the Arrhenius equation is:

      ln space k space equals space fraction numerator negative E subscript straight a over denominator R end fraction space 1 over T space plus space ln space A

      Which specific term can be calculated from an Arrhenius plot, shown below, using this equation?

      5-1-q5

      • Ea

      • begin mathsize 14px style 1 over T end style

      • R

      • begin mathsize 14px style 1 over R end style

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      11 mark

      Which concentration–time graph is correct for a reaction that is zero order with respect to a reactant?

      A blQswxWs_conc-time-graph-option-a
      B SfDyTwrV_conc-time-graph-option-b
      C 3Q~Rijan_conc-time-graph-option-c
      D juhr5Pl~_conc-time-graph-option-d

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        21 mark

        The reaction between iodine and propanone can be catalysed by sulfuric acid. The rate equation for this reaction is:

        Rate = k [H+] [C3H6O]

        Which of the following sets of statements is correct about the order of reaction with respect to each chemical involved? 

          Iodine Propanone Sulfuric acid
        A Zero First Second
        B First Zero First
        C Zero First First
        D Zero Second Zero

         

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          3
          Sme Calculator          1 mark

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

                               A + B → Products 

          The results from three different experiments carried out at a constant temperature are shown:

          Expt. 

          Initial concentration of A / mol dm-3

          Initial concentration of B / mol dm-3

          Initial rate / mol dm-3 s-1

          1

          0.30

          0.50

          6.0 x 10-4

          2

          0.30

          0.25

          1.5 x 10-4

          3

          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? 

          • 2.0 x 10-3

          • 3.2 x 10-2

          • 8.0 x 10-3

          • 2.7 x 10-2

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          41 mark

          Which rate-concentration graph is correct for a reaction that is second order with respect to a reactant?

          ocr-5-1m-q4-option-abcd

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            5
            Sme Calculator            1 mark

            A graph is plotted of ln k against 1/T.

            (k = rate constant, T = temperature in K)

            The gradient has the numerical value of −45000.

            What is the activation energy, in kJ mol−1?

            • 374

            • 374130

            • -374

            • 5.42

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            1
            Sme Calculator            1 mark

            Using the graph, what is the value of the pre-exponential factor, A, for the decomposition of N2O5?

            2N2O5(g) → 4NO(g) + O2(g)

            rates-graphs

            • 3.45 s-1

            • 31.5 s-1

            • 1.04 × 105 s-1

            • 4.79 × 1013 s-1

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            21 mark

            Acidified propanone was added to a solution of iodine. The rate equation is:

            rate = k[CH3COCH3][H+]2

            The initial rate of reaction is 2.75 x 10-3 mol dm-3

             

            CH3COCH3

            I2

            H+

            Initial concentration (mol dm-3)

            3.32

            0.25

            0.73

             

            What is the value of the rate constant?

            • 1.55 x 10-3 mol-2 dm6 s-1

            • 1.13 x 10-3 mol-2 dm6 s-1

            • 1.55 x 10-3 mol dm3 s-1

            • 1.13 x 10-3 mol dm3 s-1

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            31 mark

            The Arrhenius equation can be used to calculate the activation energy of a reaction. The gas constant, R = 8.31 J K-1 mol-1.

            bold 1 over bold T K-1

            ln k

            0.00347

            -10.9

            0.00336

            -9.7

            0.00325

            -8.5

            0.00314

            -7.3

            0.00305

            -6.1

             

            What is the activation energy for this reaction to 3 significant figures?

            • 7.62 x 10-4 kJ mol-1

            • -7.62 x 10-4 kJ mol-1

            • 90700 kJ mol-1

            • -90700 kJ mol-1

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            41 mark

            A series of experiments was carried out on a reaction involving compounds A, B and C and the following results were obtained.

            Experiment

            Initial concentration of A / mol dm-3

            Initial concentration of B / mol dm-3

            Initial concentration of C / mol dm-3

            Initial rate /
            mol dm-3 s-1

            1

            0.4

            0.12

            0.42

            3.2 x 10-3

            2

            0.8

            0.24

            0.42

            6.4 x 10-3

            3

            0.4

            0.12

            0.21

            8.0 x 10-4

            4

            1.2

            0.24

            0.84

            3.84 x 10-2

             

            What is the correct rate equation for this reaction?

            • rate = k[A][C]2

            • rate = k[A]2[B]

            • rate = k[A][B][C]2

            • rate = k[A]2[B][C]

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            51 mark

            For the reaction between nitric oxide and hydrogen, a possible reaction mechanism is shown below.

            Overall: 2NO (g) + 2H2 (g) → N2 (g) + 2H2O (l)

            Step 1: 2NO (g) → N2O2 (g)

            Step 2: N2O2 (g) + H2 (g) → H2O (l) + N2O (g)

            Step 3: N2O (g) + H2 (g) → N2 (g) + H2O (l)

            Rate = k[NO]2[H2]

            1. The rate of reaction is halved if [NO] is halved and [H2] is doubled.
            2. The second step is the rate-determining step.
            3. The rate constant is independent of temperature.

            • 1, 2 and 3

            • Only 1 and 2

            • Only 2 and 3

            • Only 1

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