IBChemistrySLExam QuestionsHow Much, How Fast & How Far?How Fast? The Rate of Chemical Change

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How Fast? The Rate of Chemical Change (SL IB Chemistry)

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How Fast? The Rate of Chemical Change

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How Fast? The Rate of Chemical Change

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11 mark

Which of the following factors will not affect the value of the activation energy of a reaction?

  1. The presence of a catalyst.
  2. Changes in temperature.
  3. Changes in the concentration of the reactants.

  • I and II only

  • I and III only

  • II and III only

  • I, II and III

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21 mark

The oxidation of butadiene, CH2=CHCH=CH2, using air or oxygen, produces the molecule crotonaldehyde, CH3CH=CHCHO.

One method of oxidation is to pass a mixture of butadiene and oxygen through a hot aqueous solution of palladium(II) ions, Pd2+(aq), which catalyse the reaction.

Which statement about the action of the Pd2+(aq) ions is not correct?

  • Pd2+(aq) lowers the activation energy for the reaction

  • Pd2+(aq) increases the energy of the reacting molecules

  • When Pd2+(aq) is used, the reaction proceeds by a different route

  • Changing the concentration of the Pd2+(aq) affects the rate of oxidation

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31 mark

The Maxwell-Boltzmann energy distribution curve below describes a mixture of two gases at a given temperature. For a reaction to occur between the gaseous molecules, they must collide with sufficient energy.

uKIVQYYV_1

Of the two activation energy (Ea) values shown, one is for a catalysed reaction, the other for an uncatalysed one.

When a catalyst is used, which pair of statements is correct?

A Ea1    uncatalysed reaction fewer effective collisions Ea2      catalysed reaction more effective collisions
B Ea1    catalysed reaction fewer effective collisions   Ea2      uncatalysed reaction more effective collisions
C Ea1      uncatalysed reaction more effective collisions Ea2      catalysed reaction fewer effective collisions
D Ea1    catalysed reaction more effective collisions Ea2      uncatalysed reaction fewer effective collisions

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    41 mark

    Ammonia is manufactured using the Haber process, which is represented by the following equation:

    N2 (g) + 3H2 (g)  rightwards harpoon over leftwards harpoon  2NH3 (g)                   ∆H = –93 kJ mol–1

    What happens to the rate of the forward and backward reactions when the temperature is increased?

    • there is no effect on the backward or forward rate 

    • both forward and backward rates increase 

    • the forward rate only increases

    • the backward rate only increases

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    51 mark

    Why does a mixture of hydrogen gas and bromine gas react together faster at a temperature of 500 K than it does at a temperature of 400 K?

    1. A higher proportion of effective collisions occurs at 500 K
    2. Hydrogen molecules and bromine molecules collide more frequently at 500 K
    3. The activation energy of the reaction is lower at 500 K

    • I and II only

    • I and III only 

    • II and III only 

    • I, II and III

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    61 mark

    When the pressure of a fixed mass of gaseous reactants is raised at a constant temperature, the rate of reaction increases.

    Which statements explain this observation?

    1. Raising the pressure lowers the activation energy.
    2. More molecules have energy greater than the activation energy at the higher pressure.
    3. More collisions occur per second when the pressure is increased.

    • I only

    • I and II only 

    • III only 

    • I, II and III

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    71 mark

    What is the main reason for the increase in reaction rate with increasing temperature?

    • The activation energy decreases.

    • The activation energy increases.

    • The molecules collide more frequently.

    • More molecules have an energy greater than the activation energy.

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    81 mark

    The diagram represents the reaction pathway for the following reaction:

    Z(g) + Y(g)  →  X(g) + W(g)

    boseFlOF_3

    What statement is true about the reverse reaction, W(g) + X(g)  →  Y(g) + Z(g)?

    • it will have a smaller activation energy and a negative ∆H 

    • it will have a smaller activation energy and a positive ∆H 

    • it will have a larger activation energy and a negative ∆H

    • it will have a larger activation energy and a positive ∆H

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    91 mark

    A student measured the rate of a reaction at two different temperatures: 40°C  and 50°C. They observed that the rate of reaction roughly doubled.

    What explains this observation?

    • raising the temperature by 10°C doubles the average velocity of the molecules 

    • raising the temperature by 10°C doubles the average kinetic energy of each molecule

    • raising the temperature by 10°C doubles the number of molecules having more than a certain minimum energy 

    • raising the temperature by 10°C doubles the number of molecular collisions in a given time

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    101 mark

    Which statements correctly describe how a catalyst works?

    1. A catalyst does not affect the enthalpy change of the reaction.
    2. A catalyst increases the rate of the reverse reaction.
    3. A catalyst increases the average kinetic energy of the reacting particles.

    • I only

    • I and II only 

    • III only 

    • I, II and III

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    11 mark

    The distribution of molecular energies in a sample of a gas at a given temperature is shown by the Boltzmann distribution graph below.

    7Be6twxH_5

    If the temperature is increased, what will happen to the position of point X?

    • fewer molecules possess the most probable energy value so X will shift to the right 

    • fewer molecules possess the most probable energy value so X will shift to the left

    • more molecules possess the most probable energy value so X will shift to the left

    • the position of X will stay the same but the area under the distribution curve increases

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    21 mark

    The diagram shows a reaction pathway for an endothermic reaction.

    Which arrow represents the activation energy for the forward reaction?

    eAOwD8WJ_8

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      31 mark

      The dotted-line curve on each graph below represents the corresponding distribution for a gas at 300 K.

      Which solid-line curve most accurately represents the distribution of molecular energies in the same gas at 500 K?

      iuQVoEiF_7

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        41 mark

        The energies of the reactants, the products and the transition state of a reaction are shown in the reaction pathway diagram below.

        rGbZAS69_9

        Which expression correctly represents how to calculate the activation energy of the forward reaction?

        • E1 – E2

        • E2 – E1

        • E2 – E3

        • E3 – E2

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        51 mark

        The diagram below represents, for a given temperature, the Boltzmann distribution of the kinetic energy of the molecules in a mixture of two gases that react slowly together without a catalyst.

        The activation energy for the reaction, Ea, is marked for the uncatalysed reaction

        What would the position of Ea be if the reaction took place with an effective catalyst?

        ydDSj_Kd_10

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          61 mark

          Four possible energy profiles are shown below, for reactions carried out at the same temperature.

          Which energy profile shows a reaction that is likely to proceed most rapidly and with a good yield?

          vKKpsGmm_11

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            71 mark

            The diagram shows a Boltzmann distribution of molecular energies for a gaseous mixture. The distribution has a peak, labelled Q on the diagram.

            gpjmU9ym_12

            What happens when an effective catalyst is added to the mixture?

            • the height of the peak remains the same, and the activation energy moves to the left 

            • the height of the peak decreases and the activation energy moves to the left

            • the height of the peak remains the same, and the activation energy moves to the right

            • the height of the peak decreases and the activation energy moves to the right

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            81 mark

            A student performs two reactions and measures the rate of product formation.

            Reaction 1: 1.5g of solid calcium carbonate is added to 100 cm3 of 0.5 M hydrochloric acid

            Reaction 2: 100 cm3 of distilled water is then added to 100 cm3 of 0.5 M hydrochloric acid then 1.5g of solid calcium carbonate is added

            The rate of reaction 1 was faster than the rate of reaction 2.

            Which of the following 3 hypotheses correctly describes the difference in the rate?

            I

            Adding water reduces the frequency of collisions between reactant molecules.

            II

            Adding water reduces the proportion of effective collisions between reactant molecules.

            III

            Adding water reduces the proportion of reactant molecules possessing the activation energy.

            • I only

            • I and II only 

            • III only 

            • I, II and III

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            91 mark

            The Boltzmann distribution shows the number of molecules that have particular kinetic energy at a constant temperature.

            oCcrHFwS_13

            If the temperature is decreased by 10 degreeC, what happens to the size of the areas labelled H, J and K?

             

            H

            J

            K

            A

            B

            C

            D

            decreases

            decreases

            increases

            increases

            decreases

            increases

            decreases

            decreases

            decreases

            decreases

            decreases

            increases

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              101 mark

              Zinc reacts with copper sulfate according to the following equation:

              Zn (s) + CuSO4 (aq) → Cu (s) + ZnSO4 (aq)

              Rates of reaction can be found by measuring how certain properties change during the course of the reaction. Which of these properties could be used?

              1. Change in volume.
              2. Change in temperature.
              3. Change in colour.

              • I and II only

              • I and III only

              • Ii and III only

              • I, II and III

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              11 mark

              In a reaction between 1M hydrochloric acid and an excess of marble chips (calcium carbonate) the volume of gas produced was measured against time. This is shown on the dotted line in the graph below.

              The experiment was repeated, but this time using the same volume of 2M hydrochloric acid. Which line on the graph represents this experiment?

              hard-1

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                21 mark

                1 dm3 of gas X and 1 dm3 of gas Y are kept at the same temperature and pressure.

                The speed of the molecules is plotted against the fraction of molecules with that speed. From the graph what can be said about the two gases?

                hard-2

                • The molar mass of X is larger than the molar mass of Y

                • The molar mass of Y is larger than the molar mass of X

                • The average kinetic energy of X is higher than that of Y

                • The average kinetic energy of Y is higher than that of X

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                31 mark

                A beaker containing 100 cm3 of 2M sulfuric acid, H2SO4 (aq), was placed on a balance and then an excess of powdered zinc was added. The change in mass was recorded against time and the results plotted on a graph as shown in line I below.

                What change in conditions could result in line II shown on the graph?

                hard-5

                • Using twice as much powdered Zn

                • Using pieces of zinc that have the same mass as the powder

                • Raising the temperature of the sulfuric acid, H2SO4 (aq)

                • Using more concentrated H2SO4 (aq), but keeping the volume the same

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                41 mark

                Bleach solution contains sodium chlorate (I) which naturally decomposes according to the equation below:

                2NaClO (aq)  → 2NaCl (aq)  +  O2 (g)

                The bleach decomposes faster as the temperature increases. A 100 cm3 sample of 10% bleach was heated to 40 degreeC and the amount of oxygen evolved was measured against time.

                The experiment was repeated under the same conditions, but this time using a 100 cm3 sample of 20% bleach. If the first experiment produces the dotted line, which line is produced by the second experiment?

                hard-6

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                  51 mark

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

                  hard-3

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                    61 mark

                    Three batches of sulfuric acid containing different volumes and concentrations were reacted with an excess of zinc powder. The hydrogen evolved was measured against time and the results were plotted on a graph. Which lines on the graph could correspond to the specified volumes and concentrations of the sulfuric acid shown in the table?

                    hard-4

                     

                     

                    25 cm3 of 1.0 M H2SO4

                    50 cm3 of 0.5 M H2SO4

                    25 cm3 of 0.5 M H2SO4

                    A

                    I

                    III

                    IV

                    B

                    I

                    IV

                    III

                    C

                    I

                    II

                    III

                    D

                    II

                    I

                    III

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                      71 mark

                      When 1 cm3 of 0.1 mol dm–3 HCl is added to 10 cm3 of 0.02 mol dm–3 Na2S2O3 solution, a pale yellow precipitate forms slowly.

                      When the experiment is repeated with 1 cm3 of 0.1 mol dm–3 HCl and 10 cm3 of 0.05 mol dm–3 Na2S2O3 the precipitate forms more quickly.

                      Why is this?

                      • when 0.05 mol dm–3 Na2S2O3 is used the reactant particles collide more frequently 

                      • when 0.05 mol dm–3 Na2S2O3 is used the collisions between reactant particles are more violent 

                      • when 0.05 mol dm–3 Na2S2O3 is used the activation energy of the reaction is lower 

                      • when 0.05 mol dm–3 Na2S2O3 is used the reaction proceeds by a different pathway 

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                      81 mark

                      On the graph, curve 1 was produced from measuring the decomposition of 100 cm3 of 1.0 mol dm–3 hydrogen peroxide in the presence of a manganese (IV) oxide catalyst.

                      hard-7

                      Which alteration to the original experimental conditions would produce curve 2?

                      • raising the temperature 

                      • adding more manganese (IV) oxide

                      • using more concentrated hydrogen peroxide 

                      • add some 0.1 mol dm–3 hydrogen peroxide

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                      91 mark

                      The stoichiometry of a catalysed reaction is shown by the equation below.

                      R (g) + S (g)  ⇌ T (g) + U (g)

                      Two experiments were carried out in which the amount of product T was measured against time. The results are shown in the diagram below.

                      5-3-ib-chemistry-mcq-q9-hard

                      Which changes in the conditions from experiment 1 to experiment 2 might explain the results shown?

                      1. Product U was continuously removed from the equilibrium mixture.
                      2. A different catalyst was used.
                      3. Less of reactant R was used

                      • I and II only

                      • I and III only

                      • II and III only

                      • I, II and III

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                      101 mark

                      Boltzmann distributions are shown in the two diagrams below.

                      hard-8

                      In diagram 1, one line, P or Q, corresponds to the activation energy in the presence of a catalyst and the other line corresponds to the activation energy of the same reaction in the absence of a catalyst.

                      In diagram 2, one curve, X or Y, corresponds to a temperature higher than that of the other curve.

                      Which combination gives the correct curve and line?

                       

                      presence of catalyst

                      higher temperature

                      A

                      B

                      C

                      D

                      P

                      P

                      Q

                      Q

                      X

                      Y

                      X

                      Y

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                        11
                        Sme Calculator                        1 mark

                        The rate information below was obtained for the following reaction of aqueous solutions of F and G, in the presence of a homogeneous catalyst, H, 

                        2F + 3G → J + 2K

                        When the concentrations of F and G are doubled, the rate of reaction increases by a factor of four.

                        When the concentrations of F and H are doubled, the rate of reaction increases by a factor of eight.

                        Which rate expression is consistent with the data?

                        • Rate = k [F]2 [G]3

                        • Rate = k [F]2 [H]

                        • Rate = k [F] [G] [H]

                        • Rate = k [F]2 [H]2

                        Choose your answer

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