IB Kinetics Q by Y7Nkt3s

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									1.   Which of the following is (are) important in determining whether a reaction occurs?

           I. Energy of the molecules

           II. Orientation of the molecules

     A.    I only

     B.    II only

     C.    Both I and II

     D.    Neither I nor II
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2.   Consider the reaction between solid CaCO3 and aqueous HCl. The reaction will be speeded up
     by an increase in which of the following conditions?

           I.       Concentration of the HCl

           II.      Size of the CaCO3 particles

           III.     Temperature

     A.    I only

     B.    I and III only

     C.    II and III only

     D.    I, II and III
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3.   The compounds with the molecular formula C4H9Br all undergo nucleophilic substitution
     reactions when warmed with sodium hydroxide solution. The equation for each of the
     reactions is

                    C4H9Br + OH–  C4H9OH + Br–

     When the reaction of one of these compounds was investigated the following kinetic data were
     obtained.

                                    Initial [C4H9Br]       Initial [OH–]         Initial rate of reaction
       Experiment number
                                       / mol dm–3           / mol dm–3              / mol dm–3 min–1
                  1                       0.010                0.010                       2.0 × 10−3
                  2                       0.020                0.010                       4.0 × 10−3
                  3                       0.020                0.020                       4.0 × 10−3




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(a)   Explain the term nucleophilic substitution.

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(b)   Deduce the order of reaction with respect to C4H9Br

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(c)   Deduce the order of reaction with respect to OH− and explain your answer.

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(d)   State the rate expression for the reaction.

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(e)   Calculate the value of the rate constant for the reaction and state its units.

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(f)   Give the equations for the mechanism of this reaction.




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     (g)     Define the term rate-determining step and identify this step in the mechanism.

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     (h)     Define the term molecularity and deduce its value in the mechanism.

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                                                                                              (Total 14 marks)



4.   The reaction between NO2 and F2 gives the following rate data at a certain temperature.
     What is the order of reaction with respect to NO2 and F2?

           [NO2]/ mol dm−3         [F2]/ mol dm–3          Rate /mol dm–3 min–
                                                                    1

                 0.1                     0.2                       0.1
                 0.2                     0.2                       0.4
                 0.1                     0.4                       0.2
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                   NO2 order                   F2 order
      A.                first                    first
      B.                first                  second
      C.               second                    first
      D.               second                  second
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5.   Which step in a multi-step reaction is the rate determining step?

     A.      The first step

     B.      The last step

     C.      The step with the lowest activation energy

     D.      The step with the highest activation energy
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6.   Excess magnesium was added to a beaker of aqueous hydrochloric acid on a balance. A graph
     of the mass of the beaker and contents was plotted against time (line 1).

               Mass




                                                                      1


                                                                      2

                                                                      Time

     What change in the experiment could give line 2?

               I.       The same mass of magnesium but in smaller pieces

               II.      The same volume of a more concentrated solution of hydrochloric acid

               III.     A lower temperature

     A.        I only

     B.        II only

     C.        III only

     D.        None of the above
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7.   The rate of a reaction between two gases increases when the temperature is increased and a
     catalyst is added. Which statements are both correct for the effect of these changes on the
     reaction?

                           Increasing the temperature                 Adding a catalyst
          A.              Collision frequency increases          Activation energy increases
          B.               Activation energy increases        Activation energy does not change
          C.            Activation energy does not change        Activation energy decreases
          D.               Activation energy increases          Collision frequency increases
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8.   The graph below shows the volume of carbon dioxide gas produced against time when excess
     calcium carbonate is added to x cm3 of 2.0 mol dm−3 hydrochloric acid.

                  Volume of CO 2




                                                              Time

     (i)    Write a balanced equation for the reaction.

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     (ii)   State and explain the change in the rate of reaction with time. Outline how you would
            determine the rate of the reaction at a particular time.

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     (iii)   Sketch the above graph on an answer sheet. On the same graph, draw the curves you
             would expect if:

             I.     the same volume (x cm3) of 1.0 mol dm−3 HCl is used.

             II.    double the volume (2x cm3) of 1.0 mol dm−3 HCl is used.

             Label the curves and explain your answer in each case.

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                                                                                                                                           (Total 10 marks)



9.   The reaction between 2-bromo-2-methylpropane (CH3CBr)3, and warm aqueous 0.100 mol
     dm−3 sodium hydroxide solution to form 2-methylpropan-2-ol, is found to have the following
     rate expression.

                              rate =k[(CH3)3CBr]

     (a)     (i)    State what is meant by the term rate of reaction.

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             (ii)   State the units for the rate constant, k.

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            (iii)    Deduce what the effect on the rate of the reaction will be if the concentration of the
                     sodium hydroxide solution is increased to 0.300 mol dm−3.

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            (iv)     Deduce the overall order of the reaction.

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            (v)      It is found that after 32.0 seconds the concentration of 2-bromo-2-methylpropane
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                     falls to 16 of its initial value. Calculate the half-life for the reaction.

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10.   The rate expression for a reaction is shown below.

                     rate = k[A]2[B]2

      Which statements are correct for this reaction?

            I.       The reaction is second order with respect to both A and B.

            II.      The overall order of the reaction is 4.

            III.     Doubling the concentration of A would have the same effect on the rate of reaction
                     as doubling the concentration of B.

      A.    I and II only

      B.    I and III only

      C.    II and III only

      D.    I, II and III
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11.   (a)   The following data were obtained for the reaction of nitrogen monoxide gas, NO(g), with
            oxygen gas to form nitrogen dioxide gas, NO2(g), at 25 C.

                                              [NO]/                       [O2]/                    Initial rate
                  Experiment                 mol dm−3                    mol dm−3                 /mol dm−3 s−1
                       1                       0.50                        0.20                     3.0 × 10−3
                       2                       0.50                        0.40                     6.0 × 10−3
                       3                       1.00                        0.80                     4.8 × 10−2

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(i)     Calculate the order with respect to the two reactants and write the rate expression
        for the reaction. Show your reasoning.

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(ii)    Explain why the following mechanism is not consistent with the rate expression.

                            NO (g) + O2 (g) → NO2(g) + O (g); slow step
                                 NO (g) + O (g) → NO2 (g); fast step

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(iii)   Explain why the following mechanism is consistent with the rate expression, but is
        unlikely.
                            2NO(g) +O2 (g) → 2NO2 (g)

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            (iv)     Explain why the following mechanism is consistent with the rate expression.

                                                   NO (g) + O2(g) → NO3 (g); fast
                                              NO3 (g) + NO (g) → 2NO2 (g); slow

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                                                                                                                                            (Total 12 marks)



12.   Based on the definition for rate of reaction, which units are used for a rate?

      A.    mol dm−3

      B.    mol time−1

      C.    dm time−1

      D.    mol dm–3 time–1
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13.   Which of the quantities in the enthalpy level diagram below is (are) affected by the use of a
      catalyst?




                                                                     I                                  II
                                        Enthalpy

                                                                                                        III



      A.    I only

      B.    III only

      C.    I and II only

      D.    II and III only
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14.   The reaction between ammonium chloride and sodium nitrite in aqueous solution can be
      represented by the following equation.

                   NH4Cl(aq) + NaNO2(aq) → N2(g) + 2H2O(l) + NaCl(aq)

      The graph below shows the volume of nitrogen gas produced at 30 second intervals from a
      mixture of ammonium chloride and sodium nitrite in aqueous solution at 20°C.

                                                    140

                                                    120

                                                    100

                                                      80
                   Volume of N 2 / cm 3
                                                      60

                                                      40

                                                      20

                                                        0
                                                            0      20 40 60               80 100 120 140 160 180
                                                                                         Time / s



      (a)   (i)    State how the rate of formation of nitrogen changes with time. Explain your answer
                   in terms of collision theory.

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            (ii)   Explain why the volume eventually remains constant.

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      (b)   (i)    State how the rate of formation of nitrogen would change if the temperature were
                   increased from 20°C to 40°C.

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            (ii)    State two reasons for the change described in (b)(i) and explain which of the two is
                    more important in causing the change.

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            (iii)   The reaction between solid ammonium chloride and aqueous sodium nitrite can
                    be represented by the following equation.

                              NH4Cl(s) + NaNO2(aq) → N2(g) + 2H2O(l) + NaCl(aq)

                    State and explain how the rate of formation of nitrogen would change if the
                    same amount of ammonium chloride were used as large lumps instead of as a
                    fine powder.

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                                                                                                                                            (Total 9 marks)



15.   What is the definition of half-life for a first order reaction?

      A.    The time required for the quantity of a reactant to decrease by half.

      B.    Half the time required for a reactant to be completely used up.

      C.    Half the time required for a reaction to reach its maximum rate.

      D.    The time required for a reaction to reach half of its maximum rate.
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16.   Values of a rate constant, k, and absolute temperature, T, can be used to determine the activation
      energy of a reaction by a graphical method. Which graph produces a straight line?

      A.    k versus T

      B.    k versus 1
                     T

      C.    ln k versus T

      D.    ln k versus 1
                        T
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17.   Nitrogen(II) oxide reacts with hydrogen as shown by the following equation.

                      2NO(g) + 2H2(g) → N2(g) + 2H2O(g)

      The table below shows how the rate of reaction varies as the reactant concentrations vary.

                                       Initial [NO] /                  Initial /[H2]mol                   Initial rate /
       Experiment                        mol dm–3                            dm–3                        mol N2 dm–3 s–1
                1                          0.100                             0.100                           2.53 × 10–6
                2                          0.100                             0.200                           5.05 × 10–6
                3                          0.200                             0.100                          10.10 × 10–6
                4                          0.300                             0.100                          22.80 × 10–6



      (a)   Determine the order of reaction with respect to NO and with respect to H2.
            Explain how you determined the order for NO.

            NO ..............................................................................................................................

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(b)   Write the rate expression for the reaction.

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(c)   Calculate the value for the rate constant, including its units.

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(d)   A suggested mechanism for this reaction is as follows.

                H2 + NO      X fast step
                X + NO → Y + H2O slow step
                Y + H2 → N2 + H2O fast step

      State and explain whether this mechanism agrees with the experimental rate expression
      in (b).

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(e)   Explain why a single step mechanism is unlikely for a reaction of this kind.

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      (f)        Deduce how the initial rate of formation of H2O(g) compares with that of N2(g) in
                 experiment 1. Explain your answer.

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                                                                                                                                                  (Total 14 marks)



18.   For a given reaction, why does the rate of reaction increase when the concentrations of the
      reactants are increased?

      A.         The frequency of the molecular collisions increases.

      B.         The activation energy increases.

      C.         The average kinetic energy of the molecules increases.

      D.         The rate constant increases.
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19.   Which statement is correct for the reaction below?

                                     4P + Q → 2R + 2S

      A.         The rate of formation of R is one half the rate of the disappearance of Q.

      B.         The rate of disappearance of Q is one quarter of the rate of disappearance of P.

      C.         The rates of formation of R and S are not equal.

      D.         The rate of formation of S is double the rate of disappearance of P.
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20.   In the Haber process for the synthesis of ammonia, what effects does the catalyst have?

                          Rate of formation of NH3(g)                            Amount of formed NH3(g)
            A.                      Increases                                           Increases
            B.                      Increases                                          Decreases
            C.                      Increases                                          No change
            D.                     No change                                            Increases
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21.   (a)   Define the term average bond enthalpy, illustrating your answer with an equation for
            methane, CH4.

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      (b)   The equation for the reaction between methane and chlorine is

                      CH4(g) + Cl2(g) → CH3Cl(g) + HCl(g)

            Use the values from Table 10 of the Data Booklet to calculate the enthalpy change for this
            reaction.

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      (c)   Explain why no reaction takes place between methane and chlorine at room
            temperature unless the reactants are sparked, exposed to UV light or heated.

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      (d)   Draw an enthalpy level diagram for this reaction.




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                                                                                                                                             (Total 10 marks)




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22.   When excess lumps of magnesium carbonate are added to dilute hydrochloric acid the following
      reaction takes place.

                  MgCO3(s) + 2HCl(aq) → MgCl2(aq) + CO2(g) + H2O(l)

      (a)   Outline two ways in which the rate of this reaction could be studied. In each case sketch a
            graph to show how the value of the chosen variable would change with time.

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      (b)   State and explain three ways in which the rate of this reaction could be increased.

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      (c)    State and explain whether the total volume of carbon dioxide gas produced would
             increase, decrease or stay the same if

             (i)    more lumps of magnesium carbonate were used.

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             (ii)   the experiments were carried out at a higher temperature.

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                                                                                                 (Total 14 marks)



23.   Carbon dioxide gas in the atmosphere reacts slightly with rainwater as shown below.

                    CO2(g) + H2O(l)        H+(aq) + HCO3−(aq)

      (i)    State the meaning of the       sign.

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      (ii)   Predict the effect, if any, of the presence of a catalyst on the acidity of rainwater. Give a
             reason for your answer.

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      (iii)   Use Le Chatelier’s principle to predict the effect of the addition of a small quantity of an
              alkali on the acidity of rainwater. Explain what effect, if any, this would have on the
              equilibrium constant, Kc.

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                                                                                                                                                 (Total 6 marks)



24.   Gaseous hydrogen iodide, HI, decomposes into its elements when heated. The decomposition
      was investigated in a series of experiments carried out at the same temperature. The following
      data was obtained.

                                                                                      −3
                                                      Initial (HI) / mol dm
        Experiment number                                                                     Initial rate of reaction / mol dm−3 s−1
                       1                                    2.2 × 10−3                                              1.1 × 10−6
                       2                                    6.6 × 10−3                                              9.9 × 10−6
                       3                                    2.2 × 10−2                                              1.1 × 10−4
                       4                                    4.4 × 10−3                                          to be determined



      (a)     Write the equation for the decomposition of hydrogen iodide.

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      (b)     Deduce the order of the reaction and explain your answer.

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      (c)     State the rate expression for the reaction.

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      (d)   Determine the initial rate of reaction in experiment 4.

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      (e)   Define the term molecularity and deduce its value in this reaction.

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                                                                                                                                               (Total 7 marks)




25.   The enthalpy change, ∆Hο, for a chemical reaction is −10 kJ mol−1 and the entropy change, ∆Sο,
      is −10 J K–1 mol–1 at 27°C. What is the value of ∆Gο(in J) for this reaction?

      A.    −260

      B.    −7000

      C.    −9730

      D.    −13000
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26.   For a given reaction, why does the rate of reaction increase when the concentrations of the
      reactants are increased?

      A.    The frequency of the molecular collisions increases.

      B.    The activation energy increases.

      C.    The average kinetic energy of the molecules increases.

      D.    The rate constant increases.
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27.   Consider the following statements.

            I.        The rate constant of a reaction increases with increase in temperature.

            II.       Increase in temperature decreases the activation energy of the reaction.

                                                                                                 Ea
            III.  The term A in the Arrhenius equation ( k  Ae RT ) relates to the energy
                  requirements of the collisions.
      Which statement(s) is/are correct?

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      A.    I only

      B.    II only

      C.    I and III only

      D.    II and III only
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28.   For the chemical reaction

                     2NO(g) + O2(g) → 2NO2(g)

      the following reaction mechanism has been proposed.

                     NO (g) + NO(g)      N2O2 (g)            fast
                     N2O2 (g) + O2 (g) → 2NO2 (g)            slow

      What could be the rate expression for this reaction?

      A.    rate = k[NO][O2]

      B.    rate = k[NO]2

      C.    rate = k[N2O2][O2]

      D.    rate = k[NO]2[O2]
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29.   Oxygen and nitrogen monoxide react together to form nitrogen dioxide.

                     O2(g) + 2NO(g) → 2NO2(g)

      The graph below shows how the initial rate of reaction changed during an experiment in which
      the initial [NO(g)] was kept constant whilst the initial [O2(g)] was varied.




                          Rate




                                                    [O 2 (g)]




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(a)   Deduce, giving a reason, the order of reaction with respect to O2

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(b)   In a series of experiments, the initial [O2(g)] was kept constant while the initial [NO(g)]
      was varied. The results showed that the reaction was second order with respect to NO.
      Sketch a graph to show how the rate of reaction would change if the initial
      [NO(g)] was increased.

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(c)   Deduce the overall order of this reaction.

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(d)   State and explain what would happen to the initial rate of reaction if the initial
      concentration of NO was doubled and that of O2 was halved.

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      (e)   When the initial values are [O2(g)] = 1.0 × 10−2 mol dm–3 and [NO(g)] = 3.0 × 10−2 mol
            dm–3, the initial rate of reaction is 6.3 × 10−4 mol dm–3s–1. Write the rate expression for
            this reaction and calculate the rate constant, stating its units.

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                                                                                               (Total 12 marks)



30.   (a)   Nitrogen monoxide may also be converted into nitrogen dioxide at high temperature
            according to the equation below.

                                NO(g) + CO(g) + O2(g) → NO2(g) + CO2(g)

            (i)   Sketch a graph of concentration of NO2(g) produced against time for this reaction
                  and annotate the graph to show how the initial rate of reaction could be deduced.

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      (ii)   The results from a series of experiments for this reaction are shown below.
             Deduce, giving a reason, the order of reaction with respect to each of the reactants.

                                [NO(g)] /        [CO(g)] /        [O2(g)] /      Initial rate /
              Experiment
                                mol dm−3         mol dm−3         mol dm−3       mol dm−3 s−1
                    1           1.00 × 10−3      1.00 × 10−3     1.00 × 10−1      4.40 × 10−4
                    2           2.00 × 10−3      1.00 × 10−3     1.00 × 10−1      1.76 × 10−3
                    3           2.00 × 10−3      2.00 × 10−3     1.00 × 10−1      1.76 × 10−3
                    4           4.00 × 10−3      1.00 × 10−3     2.00 × 10−1      7.04 × 10−3

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(b)   Explain why the order of a reaction cannot be obtained directly from the stoichiometric
      equation.

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(c)   (i)    First order reactions have a constant half-life. Define the term half-life and explain
             why it is constant for first order reactions.

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            (ii)      The value of k for a first order reaction is 440 s−1. Calculate the half-life for this
                      reaction.

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                                                                                                                                             (Total 13 marks)



31.   Which step is included in the definition of the term rate determining step?

      A.    the step with the slowest moving particles

      B.    the step with the fewest reactant particles

      C.    the slowest step in a reaction

      D.    the last step in a reaction
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32.   (a)   Identify two features of colliding molecules that react together in the gas phase.

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      (b)   For many reactions, the rate approximately doubles for a 10°C rise in temperature.
            State two reasons for this increase and identify which of the two is the more important.

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                                                                                                                                               (Total 5 marks)




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33.   The rate expression for a particular reaction is

                      Rate = k[P][Q]

      Which of the units below is a possible unit for k?

      A.    mol–2 dm6 min–1

      B.    mol–1 dm3 min–1

      C.    mol dm3 min–1

      D.    mol–2 dm–6 min–1
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34.   Which statement is correct about the behaviour of a catalyst in a reversible reaction?

      A.    It decreases the enthalpy change of the forward reaction.

      B.    It increases the enthalpy change of the reverse reaction.

      C.    It decreases the activation energy of the forward reaction.

      D.    It increases the activation energy of the reverse reaction.
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35.   The following reaction

                      2N2O5(g) → 4NO2(g) + O2 (g)

      is described as first order with respect to N2O5.

      (a)   Write the rate expression for the reaction.

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                                                                                                                                                     (1)

      (b)   One possible mechanism for this reaction is given below.

                      N2O5(g) → NO(g) + NO3(g)                                                Step 1

                      N2O5(g) + NO3(g) → 2NO2(g) + O2(g)                                      Step 2

            Describe the rate expression that would result if the rate determining step in the
            mechanism is




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      (i)       Step 1.

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      (ii)      Step 2.

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      Outline your reasoning.

(c)   Explain what is meant by the term half-life for this reaction.

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(d)   State what is characteristic about the half-life of a first order reaction.

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                                                                                                                                         (Total 6 marks)




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