Topic 9 – Kinetics - Questions

Q1.The gas phase reaction between hydrogen and iodine is reversible.

H2(g) + I2(g) 2HI(g)

(a)  (i)  Write the expression for the equilibrium constant, Kc, for this reaction.

(1)

(ii)  If the starting concentration of both hydrogen and iodine was a mol dm−3 and it was found that 2y mol dm−3 of hydrogen iodide had formed once equilibrium had been established, write the Kc expression in terms of a and y.

(2)

(b)  The expression for the equilibrium constant in (a)(ii) can be rearranged as shown.

In an experiment, air was removed from a 1 dm3 flask and amounts of hydrogen and iodine gases were mixed together such that their initial concentrations were both a mol dm−3. This mixture was allowed to reach equilibrium at 760 K. The equilibrium concentration of iodine was then measured.

The experiment was repeated for various initial concentrations, a mol dm−3, and the results recorded in the table.

(i)  Complete the table to give the two remaining values of y mol dm−3, to two decimal places.

(1)

(ii)  Plot a graph to show how y mol dm−3 varies with the initial concentrations of hydrogen and iodine, a mol dm−3.

(2)

(iii)  Determine the gradient of your graph.

Show your working on the graph.

(2)

(iv)  Use your answer to (b)(iii) and the expression to calculate the value of Kc.

(2)

(c)  Identify a safety issue associated with this experiment.

(1)

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(d)  One of the experiments in part (b) was repeated using the same molar quantities of hydrogen and iodine but in a 500 cm3 flask instead of the 1 dm3 flask.

Deduce the effect, if any, that this would have on the rate of reaction and on the value of Kc calculated.

(2)

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(e)  The equation for the reaction between hydrogen and iodine is

H2(g) + I2(g) 2HI(g)          ΔH = –9.6 kJ mol−1

(i)  Explain the effect, if any, on the value of Kc when the temperature is increased.

(2)

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(ii)  On your graph in (b)(ii), draw and label the line you would expect if the experiment was carried out at 1000 K instead of 760 K.

(1)

(Total for question = 16 marks)

 Q2.(a)  Sea water is a source of chemicals. The most abundant chemical dissolved in sea water is sodium chloride. Compounds of magnesium and bromine are also present. Magnesium occurs at 1300 parts per million (ppm) and bromine at 60 ppm by mass.

The solution left after crystallizing sodium chloride from sea water is even richer in bromine, and contains around 2.2 g dm−3 of bromine.

Bromine is extracted from this solution by passing in chlorine gas. The mixture is acidified to prevent hydrolysis of bromine by the reaction

Br2(aq) + H2O(l) 2H+(aq) + Br−(aq) + BrO−(aq)

The bromine can be separated by heating the solution to collect bromine vapour which is then condensed, or by blowing air through the solution.

(i)  Show by calculation that a solution containing 2.2 g dm−3 of bromine is richer in bromine than one containing 60 ppm.

[Assume that the mass of 1 dm3 of the bromine solution is 1000 g]

(1)

(ii)  Write an ionic equation, including state symbols, for the reaction in which chlorine gas reacts with bromide ions in solution to produce bromine.

(2)

(iii)  What would be observed when the reaction in (ii) occurs?

(1)

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(iv)  Explain why the addition of an acid, such as hydrochloric acid, prevents hydrolysis of bromine.

(2)

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(v)  Assuming the hydrolysis of bromine is endothermic, explain how an increase in temperature would affect the equilibrium position for the hydrolysis of bromine.

(2)

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(vi)  Use your knowledge of activation energy to explain why an increase in temperature increases the rate of hydrolysis of bromine.

(1)

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(vii) Use the equation for the hydrolysis of bromine to show that it is a disproportionation reaction.

Br2(aq) + H2O(l) 2H+(aq) + Br−(aq) + BrO−(aq)

(2)

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(b) At the surface of the sea, there is a dynamic equilibrium between carbon dioxide gas in air and dissolved carbon dioxide in the surface sea water.

CO2(g) CO2(aq)

(i)  State two features of a system which has reached dynamic equilibrium.

(2)

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*(ii)  Carbon dioxide dissolves more easily in seawater than in pure water because seawater contains carbonate ions, CO32−(aq), and the following reaction occurs.

CO2(aq) + H2O(l) + CO32−(aq) 2HCO3 −(aq)

Explain how an increase in concentration of carbonate ions in sea water affects the amount of carbon dioxide gas in the atmosphere.

(2)

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(iii)  Carbon dioxide and water vapour both contain polar bonds.

What effect does infrared radiation have on the bonds in these molecules?

(1)

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*(iv)  Outline the mechanism by which molecules such as carbon dioxide and water cause global warming.

(2)

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*(v) Without water vapour in the atmosphere, the earth would be many degrees colder than it is at present. Why are many climate change scientists more concerned about warming due to carbon dioxide in the atmosphere, than warming due to the presence of water vapour? Refer to the difference between anthropogenic climate change and natural climate change in your answer.

(4)

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(Total for Question = 22 marks)

Q3.

The compound sulfuryl chloride is a colourless liquid with the formula SO2Cl2.

It decomposes at room temperature to form sulfur dioxide and chlorine.

The rate of the decomposition of SO2Cl2 can be investigated by monitoring the concentration of SO2Cl2 as the reaction proceeds. The data in the table were collected from such a reaction.

(i)  Plot a graph of these results.

(3)

(ii)  Determine the order of reaction with respect to SO2Cl2 and hence write the rate equation for the reaction. Show on your graph how you arrived at your answer.

(3)

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(iii)  Use your graph to find the rate of reaction when the concentration of SO2Cl2 is 0.200 mol dm−3.

Hence calculate the rate constant, k, to an appropriate number of significant figures. Include units in your answer.

(4)

(b)  Write a possible two-step mechanism for the reaction that is consistent with your rate equation and clearly identify the rate-determining step.

(2)

 

(Total for question = 12 marks)

 Q4.

This question is about the kinetics of chemical reactions.

Catalysts are sometimes used in reactions.

(i)   Explain how a catalyst affects the rate of a reaction.(3)

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(ii)   Draw and label lines on the axes to show how an increase in temperature affects the number of particles with E > Ea.

(2)

Q5. 

Ammonia is used in the manufacture of nitric acid.

The equation for one step in this manufacturing process is:

4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g)   = −900 kJ mol−1

*(a)   A manufacturer carries out this reaction at a temperature of 1200 K and a pressure of 10 atm. A scientist proposes that a temperature of 1000 K should be used at the same pressure.

Evaluate the effects of making this change on the rate and yield of this reaction.

(6)

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*(b)   When this reaction is used in industry, the catalyst is an alloy of platinum and rhodium.

The diagram shows the reaction profile for the uncatalysed reaction.

(i)   On the diagram, draw the reaction profile for the catalysed reaction.

(1)

(ii)   Label the diagram to show

the enthalpy change, Hthe activation energy, Eafor the catalysed reaction.

(2)

(c)   Write the expression for the equilibrium constant, Kc, for this reaction.

(1)

Q6. 

This question is about the effect of changes in temperature on reactions.

* Compound X reacted reversibly with concentrated sulfuric acid to form two isomers, A and B.

compound X + H2SO4(conc.) isomer A + isomer B

At 40°C, approximately 95% of the product was isomer A. At 160 °C, the product contained approximately 85% of isomer B.

The diagram shows the reaction profiles for the formation of the two isomers.

Use the information to comment on the different yields of isomer A and isomer B at different temperatures.

(6)

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Q7. 

This question is about the oxidation of ammonia.

In fact, this oxidation to form nitrogen(II) oxide is an equilibrium reaction.

(i)  Explain the effect, if any, of increasing pressure on the equilibrium yield of NO in this reaction.

(2)

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(ii)  Explain the effect, if any, of an increase in pressure on the rate of this reaction.

(2)

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(iii)  The platinum-rhodium catalyst used in this reaction is a heterogeneous catalyst. State what is meant by the term 'heterogeneous' and why a catalyst has no effect on the yield of the products in the reaction.

(2)

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(Total for question = 6 marks)

 

Q8. 

This question is about the decomposition of hydrogen iodide.

The decomposition of hydrogen iodide is catalysed by the heterogeneous catalyst platinum.

(a)  State the meaning of the term heterogeneous.

(1)

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(b)  (i)  Label the axes and draw a curve to show the Maxwell-Boltzmann distribution of molecular energies in a gas. Mark on your graph a suitable value for the activation energy, Ea , for the reaction.

(3)

(ii)  Use the Maxwell-Boltzmann distribution to explain why a catalyst increases the rate of a reaction.

(3)

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Q9. 

The solid compound V2O5 is used as a heterogenous catalyst in industry to speed up the reaction between oxygen and sulfur dioxide gas.

The reaction has two stages:

Stage 1        SO2(g) + V2O5(s) → SO3(g) + 2VO2(s)

Stage 2        2VO2(s) + ½O2(g) → V2O5(s)

(i)  Write the equation for the overall reaction. State symbols are not required.

(1)

*(ii)  Explain the catalytic behaviour of V2O5 in this reaction.

(6)

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Q10. 

This question is about transition metals.

Manganate(VII) ions, react with ethanedioate ions in acid solution.

The reaction starts slowly, the rate of reaction then increases, before it decreases again.

Explain this sequence.

(3)

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(Total for question = 3 marks)

 

Q11. 

The diagram below shows the Maxwell-Boltzmann distribution of molecular energies for a catalysed reaction.

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(a)  If the temperature were lowered, what would be the effect on the shape of the curve?

(1)

   A    The peak would shift to the left and be higher.

   B    The peak would shift to the left and be lower.

   C    The peak would shift to the right and be higher.

   D    The peak would shift to the right and be lower.

(b)  Which of the following would shift the activation energy line to the right?

(1)

   A    An increase in reactant concentration.

   B    The removal of the product.

   C    The removal of the catalyst.

   D    The use of smaller particles with a larger surface area.

 

(Total for question = 2 marks)

Q12. 

This question concerns alkenes and some halogen compounds.

Chloroethene can be manufactured by a two-stage process.

(i)  In stage 1, chlorine is reacted with ethene at a temperature between 50 °C and 80 °C

Give one reason why a temperature below 50 °C and another reason, apart from costs, why a temperature above 80 °C would not be used for this process.

(2)

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(ii)  In stage 2, the product from the first reaction is converted to chloroethene:

Both products are required for use in other processes. Which method would be most suitable for the separation of these two products?

(1)

   A    fractional distillation

   B    solvent extraction using a separating funnel

   C    heating under reflux

   D    bubble through dilute alkali

 

(Total for question = 3 marks)

 

Q13. 

The graph shows the Maxwell-Boltzmann distribution of molecular energies of a gaseous system.

(i)   On the graph, draw the Maxwell-Boltzmann distribution for the same system at a higher temperature.

(1)

(ii)  Use the graph to explain why a small increase in temperature results in a large increase in the rate of a gaseous reaction.

(3)

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(Total for question = 4 marks)

 

Q14. 

This question is about the kinetics of chemical reactions.

A reaction between iodine and propanone, in the presence of hydrogen ions, has the rate equation:

rate = k[CH3COCH3][H+]

(i)   Give the overall order of the reaction.

(1)

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(ii)   Explain, in terms of collision theory, why increasing the concentration of propanone changes the rate of reaction.

(2)

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Q15. 

Bromate(V) ions, BrO3−, oxidize bromide ions, Br−, in the presence of dilute acid, H+, as shown in the equation below.

Three experiments were carried out using different initial concentrations of the three reactants.

The initial rate of reaction was calculated for each experiment.

The results are shown in the table below.

*(a)  (i)   This reaction is first order with respect to BrO3−(aq).  State, with reasons, including appropriate experiment numbers, the order of reaction with respect to

(5)

H+(aq)

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Br−(aq)

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(ii)   Write the rate equation for the reaction.

(1)

(iii)   Use the data from experiment 1 and your answer to (a)(ii) to calculate the value of the rate constant.  Include units in your answer.

(3)

(b)  What evidence suggests that this reaction proceeds by more than one step?

(1)

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(c)  The initial rate of reaction was obtained from measurements of the concentration of bromine at regular time intervals.  How is the initial rate of formation of bromine calculated from a concentration-time graph?

(2)

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(Total for question = 12 marks)

Q16.This question is about the elimination of hydrogen bromide from bromoalkanes by reaction with alcoholic potassium hydroxide.

C4H9Br + KOH → C4H8 + KBr + H2O

To investigate the kinetics of this reaction the following apparatus was used:

A solution of concentrated potassium hydroxide in ethanol was refluxed and the gas syringe connected as shown.

0.6 cm3 of 1-bromobutane was added to the solution with a hypodermic syringe through a rubber seal.

A stop clock was started and the volume of gas, Vt, measured at 2 minute intervals, for 12 minutes. When there was no further evolution of gas the volume of gas, Vfinal, was 76.5 cm3.

(a)  (i)  Calculate the number of moles of 1-bromobutane used. You will need the values of the density and molar mass of 1-bromobutane from your Data booklet.

(2)

(ii)  Calculate the maximum volume of gaseous but-1-ene, in cm3, that could form.

[Molar volume of a gas 24 000 cm3 under reaction conditions]

Suggest two reasons why this volume is unlikely to form.

(3)

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(b)  The results obtained are shown in the table below.

(i)  Explain why a large excess of potassium hydroxide is used in this experiment.

(1)

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(ii)  Plot a graph of (Vfinal − Vt)/cm3 against t/min.

(3)

(iii)  Suggest why the value of (Vfinal − Vt) was plotted on your graph.

(1)

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(iv)  Measure two successive half lives from your graph.

(2)

First half life     ......................................................................................................................................... min

Second half life ......................................................................................................................................... min

(v)  Deduce the order of reaction with respect to 1-bromobutane.

Justify your answer.

(2)

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(c)  In another experiment, an excess of 1-bromobutane is reacted with varying concentrations of hydroxide ions. The results for the initial rate of the reaction are shown in the table below.

(i)  Deduce the order of reaction with respect to hydroxide ions. Justify your answer using the data in the table.

(2)

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(ii)  Write the rate equation for the reaction using your answers to parts (b)(v) and (c)(i).

(1)

(iii)  Give the units of the rate constant.

(1)

*(iv)  It is suggested that the reaction begins with the slow attack by a hydroxide ion on a hydrogen atom in the 1-bromobutane, as shown below.

Complete the electron pair movement for this reaction using curly arrows and explain why this step is consistent with the rate equation for the reaction you have given in (c)(ii).

(3)

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(Total for Question = 21 marks)

Q17.The ionic equation for the reaction of ammonium peroxodisulfate (persulfate), (NH4)2S2O8, with potassium iodide, KI, is

S2O82−(aq) + 2I−(aq) → 2SO42−(aq) + I2(aq)

(a)  In a series of experiments to determine the rate equation for this reaction, 10 cm3 of 0.0050 mol dm−3 sodium thiosulfate was mixed with 20 cm3 of (NH4)2S2O8 solution and 5 drops of starch solution. 20 cm3 of KI solution was added with mixing and the time taken for the solution to darken was noted. The initial concentrations of the (NH4)2S2O8 and KI solutions and the times for the mixture to darken are shown below.

(i)  Explain the purpose of the sodium thiosulfate solution.

(2)

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(ii)  Use the data in the table to deduce the rate equation for the reaction between S2O82− and I− ions. Explain, by referring to the data, how you arrived at your answer.

(3)

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(b)  A further experiment was carried out to confirm the order of the reaction with respect to iodide ions. (NH4)2S2O8 was mixed with KI to form a solution in which the initial concentration of (NH4)2S2O8 was 2.0 mol dm−3 and that of KI was 0.025 mol dm−3. The concentration of iodine was measured at various times until the reaction was complete.

(i)  Outline a method, not involving sampling the mixture, which would be suitable for measuring the iodine concentrations in this experiment. Experimental details are not required but you should state how you would use your measurements to obtain iodine concentrations.

(3)

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(ii)  Explain why the initial concentration of (NH4)2S2O8 is much higher than that of KI.

(1)

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(iii)  State how the initial rate of reaction may be obtained from the results of this type of experiment.

(2)

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(iv)  In such an experiment a student calculated the initial rate of reaction to be 8.75 × 10−5 mol dm−3 s−1. Use this value, the initial concentrations in (b) and the rate equation that you obtained in (a)(ii), to calculate the rate constant for this reaction. Include units in your answer.

(2)

(c)  Using the method outlined in (b), the rate constant for this reaction was determined at various temperatures. The data from these experiments are shown in the table below. Note that none of the temperatures corresponds to that used in (b) and that the rate constant is given in appropriate units.

(i)  Use the data in the table to plot a graph of ln k (on the y axis) against 1/T (on the x axis) and draw a best fit line through the points.

(2)

(ii)  Determine the gradient of the best fit line in (c)(i) and use this value to calculate the activation energy, Ea, of the reaction, stating the units.

(4)

The rate constant of a reaction, k, is related to the temperature, T, by the expression

(Total for Question = 19 marks)

Q18. 

*  An excess of magnesium was added to 100 cm3 of 0.0540 mol dm−3 HCl(aq). The same mass of magnesium, from the same sample, was added to 100 cm3 of 0.0540 mol dm−3 HCOOH(aq).

Both reactions were carried out at the same temperature. Compare and contrast the total volume of hydrogen evolved, and the rate at which it will be evolved, in the two reactions.

(6)

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Q19. 

One of the stages in the production of sulfuric acid from sulfide ores involves the oxidation of sulfur dioxide to sulfur trioxide. The equation for the reaction is

2SO2(g) + O2(g) 2SO3(g)      ΔrH = –197 kJ mol–1

The conditions used in one industrial process are: 420°C and a pressure of 1.7 atm together with a vanadium(V) oxide catalyst.

It is proposed to change the conditions to 600°C and 10 atm pressure, while still using the same catalyst.

(i)  On the axes provided, sketch the reaction profiles for the uncatalysed and catalysed reaction.

2SO2(g) + O2(g) 2SO3(g)      ΔrH = –197 kJ mol–1

Label the uncatalysed reaction, A, and the reaction catalysed by vanadium(V) oxide, B.

(3)

(ii)  On your reaction profile, identify and label both the enthalpy change and the activation energy for the catalysed reaction.

(2)

 

(Total for question = 5 marks)

 

Q20. 

Many vehicles are fitted with airbags which provide a gas-filled safety cushion to protect the occupant of the vehicle if there is a crash.

(a)  The first reaction in airbags is the thermal decomposition of sodium azide, NaN3, to form sodium and nitrogen gas.

(i)  Write the equation for this decomposition of sodium azide.

State symbols are not required.

(1)

(ii)  In the reaction in (i), a typical airbag is inflated by about 67 dm3 of gas.

Calculate the minimum mass of sodium azide, in grams, needed to produce this volume of gas. Use the Ideal Gas Equation and give your answer to an appropriate number of significant figures.

For the purpose of this calculation, assume that the temperature is 300 °C and the pressure is 140 000 Pa.

(4)

(b)  The second reaction in the airbag is between the sodium produced in the reaction (a)(i)  and potassium nitrate.

Balance the above equation, justifying your answer in terms of the changes in oxidation numbers.

(3)

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(c)  The third reaction in the airbag is between the metal oxides and silicon dioxide.

State the type of reaction taking place and justify why this reaction is necessary.

(3)

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(d)  The Maxwell-Boltzmann distribution diagram shows the molecular energies for the gaseous system immediately after the airbag has been deployed.

What is the change in shape of the curve when the airbag cools?

(1)

   A    the peak would shift to the left and be higher

   B    the peak would shift to the left and be lower

   C    the peak would shift to the right and be higher

   D    the peak would shift to the right and be lower

 

(Total for question = 12 marks)

 

Q21. 

Nichrome is an alloy used to make wires for electrical heating elements.

An investigation is carried out into the resistance to corrosion of two types of nichrome. The table shows their compositions by mass.

Nickel and chromium both react with hydrochloric acid to form a salt and hydrogen. Both nichromes contain nickel and chromium in the ratio 4:1 by mass.

In one experiment, a sample of nichrome A was added to hydrochloric acid, and the hydrogen gas formed was collected. Its volume was measured over a period of time.

(a)  Which is a correct equation for the reaction between nickel and hydrochloric acid to form nickel(II) chloride?

(1)

   A    2Ni(s) + 2HCl(aq) → 2NiCl(aq) + H2(g)

   B    2Ni(s) + 2HCl(l) → 2NiCl(aq) + H2(g)

   C    Ni(s) + 2HCl(aq) → NiCl2(aq) + H2(g)

   D    Ni(s) + 2HCl(l) → NiCl2(aq) + H2(g)

(b)  The graph shows the results obtained when nichrome A reacts with hydrochloric acid.

(i)  Draw a tangent to the curve on this graph, at t1 = 6.5min.

Calculate the rate of reaction at t1. Include units in your answer.

(3)

(ii)  The rate of reaction at t2 = 24.5 min is lower.

Give reasons why the rates of reaction at t1 and t2 differ.

You should assume that the temperature of the reaction mixture does not change during the experiment.

(2)

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*(c)  It was suggested that nichrome B has a lower resistance to corrosion because the copper in it might act as a catalyst in the reactions of nickel and chromium with hydrochloric acid.

Devise a method a scientist could use to find out whether copper acts as a catalyst or a reactant in these reactions of nichrome B.

(6)

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(Total for question = 12 marks)

 

Q22. 

This question is about the thermal decomposition of ammonia.

This reaction is catalysed by platinum and is represented by the equation:

2NH3(g) → N2(g) + 3H2(g)     = + 92 kJ mol−1

The diagram shows a sketch of the Maxwell-Boltzmann curve for the distribution of molecular energies for a fixed amount of ammonia gas at a given temperature.

Ea represents the activation energy of the uncatalysed reaction.

(i)   On the diagram, draw a vertical line to represent the activation energy of the catalysed reaction. Label this line Ea (with catalyst).

(1)

(ii)   Use the diagram to explain why the use of a catalyst increases the rate of decomposition of ammonia.

(3)

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Q23. 

This question concerns the Maxwell-Boltzmann energy distribution shown below.

(a)  What is the best way to describe the activation energy, Ea, of a reaction?

(1)

   A    The average energy of the particles that react.

   B    The minimum energy required for a reaction to occur.

   C    The energy difference between the reactants and products.

   D    The energy produced by the particles that react.

(b)  How does the curve above change when the temperature is increased?

(1)

   A    The peak increases in height and moves to the left.

   B    The peak increases in height and moves to the right.

   C    The peak decreases in height and moves to the left.

   D    The peak decreases in height and moves to the right.

(c)  What would be the effect on the diagram if the reactant concentrations were increased?

(1)

   A    There would be no change.

   B    The Ea line would move to the right.

   C    The Ea line would move to the left.

   D    The peak decreases in height and moves to the right.

(d)  What would be the effect on the diagram if a catalyst was added? The activation energy would

(1)

   A    be unchanged and the peak would move to the right.

   B    move to the left and the peak would move to the right.

   C    move to the left and the peak would move to the left.

   D    move to the left and the peak would be unchanged.

 

(Total for question = 4 marks)

 

Q24. 

The kinetics of the fast reaction below were investigated in a series of experiments.

(a)  Outline a titrimetric method that could be used to measure the change in concentration of compound A with time. Compound A is an alkali, whereas compounds B, C and D are neutral.

(3)

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(b)  The rate of the reaction was measured at several different concentrations of A, in the presence of a large excess of compound B and a constant amount of catalyst X, to find the order of reaction with respect to A. The results are shown on the graph below.

(i)  Explain how the graph confirms that the reaction is first order with respect to A.

(1)

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(ii)  Suggest an explanation, other than human error, for the two anomalous results circled on the graph.

(3)

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(c)  In a second series of experiments, further data were collected using an initial rates method. These results are summarised in the table below.

(i)  Give one reason why obtaining these further data may be considered useful.

(1)

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(ii)  Deduce the rate equation for this reaction, explaining how you arrived at your answer.

(5)

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(iii)  Use your answer from (c)(ii), and appropriate data from Experiment 4, to calculate the value of the rate constant, k. Include units in your answer.

(2)

 

(Total for question = 15 marks)

 

Q25. 

This question is about the oxidation of ammonia.

The diagram shows a Maxwell-Boltzmann distribution of particle energies, including the activation energy, Ea , for a reaction.

(1)

An increase in temperature will

(1)

   A    increase the area under the curve.

   B    move the peak of the curve to the right.

   C    raise the height of the peak.

   D    move the position of the activation energy, Ea , to the left.

 

(Total for question = 2 marks)

 

Q26.

The energy marked X in the Maxwell-Boltzmann distribution shows

   A    the most common energy of the molecules.

   B    the activation energy of the reaction.

   C    the activation energy of a catalysed reaction.

   D    the number of molecules with energy greater than the activation energy.

(Total for Question = 1 mark)

Q27. 

The reaction of heated magnesium with steam is faster than the reaction of magnesium with cold water.  This is mainly because

   A     in cold water, the water molecules do not collide as frequently with magnesium.

   B     the coating of oxide on magnesium decomposes when it is heated.

   C     the fraction of particles with energy greater than the activation energy is higher                in the reaction with steam.

   D     the reaction with steam goes by an alternative route with lower activation energy.

(Total for question = 1 mark)

Q28. 

This question is about how catalysts work.

Gaseous reactants attach to the catalytic surface by the process of

(1)

   A    absorption

   B    activation

   C    adsorption

   D    desorption

 

(Total for question = 1 mark)

 

Q29. 

Which of the following will not affect the rate of the reaction below?

CaCO3(s) + 2HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g)

   A    Surface area

   B    Concentration

   C    Pressure

   D    Temperature

 

(Total for question = 1 mark)

Q30. 

Which of the arrows, A, B, C, D, indicates the activation energy for a catalysed reaction on the reaction profile shown?

   A   

   B   

   C   

   D   

 

(Total for question = 1 mark)

Q31.In the industrial process involving gas phase reactions to produce ammonia, many collisions between molecules are unsuccessful because

   A    gas phase reactions are reversible.

   B    the collisions are not energetic enough to break the bonds in the molecules.

   C    gas phase reactions can only occur when a catalyst is present.

   D    gas phase reactions can only occur when UV light is present.

(Total for Question = 1 mark)

Q32. 

This is a question about catalytic converters in car exhaust systems.

Which area in the Maxwell-Boltzmann distribution diagram represents the increase in the number of particles with sufficient energy to react in the presence of a catalyst?

(1)

   A    area A

   B    area B

   C    area A − area B

   D    area A + area B

 

(Total for question = 1 mark)