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A LevelChemistryEdexcelExam Questions5. Advanced Physical Chemistry (A Level Only)5.5 Kinetics II

Kinetics II (Edexcel A Level Chemistry)

Exam Questions

2 hours9 questions
Medium
Hard
1a1 mark

This question is about the compound potassium bromate, KBrO3 .

These bromate ions react with bromide ions in acidic solution.

BrO3−(aq) + 5Br−(aq) + 6H+(aq) → 3Br2(aq) + 3H2O(l)

i)
Explain, in terms of oxidation numbers, whether or not this is a disproportionation reaction.
(2)

ii)
What is the overall order of this reaction?

(1)

 

☐

A

3

 

☐

B

6

 

☐

C

12

 

☐

D

cannot tell from this information

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1b
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Potassium bromate decomposes on heating.

2KBrO3 → 2KBr + 3O2

Calculate the maximum volume of oxygen, in dm3, measured at room temperature and pressure (r.t.p.), that could be produced from the complete decomposition of 5.20 g of potassium bromate.
[Molar volume of gas at r.t.p. = 24.0 dm3 mol−1]

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2a2 marks

This question is about carbon monoxide, CO, which is a toxic and colourless gas used widely in the chemical industry.

Draw a dot-and-cross diagram of a molecule of carbon monoxide.

Use dots (•) for the carbon electrons and crosses (×) for the oxygen electrons.

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2b
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Carbon monoxide can be made by the thermal decomposition of sodium ethanedioate.

Na2C2O4 → Na2CO3 + CO

Calculate the atom economy, by mass, for the production of carbon monoxide in this reaction.

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2c
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Carbon monoxide can also be made by the thermal decomposition of ethanal, CH3CHO, in the gas phase.

CH3CHO (g) → CH4 (g) + CO (g)

This reaction was carried out at two different temperatures, and all other variables were kept constant.

Temperature / K Rate / mol dm−3 s−1 1/Temperature (1/T) / K−1 ln rate
700 0.0108 1.43 × 10−3  
850 4.90   1.59

i)
Complete the data in the table.

(1)

ii)
Calculate the activation energy, Ea, for the reaction without plotting a graph.
Include a sign and units in your answer.

The Arrhenius equation may be written as

      In rate = − E subscript a over R italic cross times italic 1 over T + constant                      [R = 8.31 J mol−1 K−1]

(3)

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2d
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Haemoglobin (Hb) found in red blood cells reacts almost irreversibly with carbon monoxide.
Initial rate experiments were carried out to investigate the effect of the concentrations of Hb and CO on the rate of this reaction.

Experiment [Hb] / mol dm−3 [CO] / mol dm–3 Rate / mol dm−3 s−1
1 2.09 × 10–6 1.40 × 10–6 8.20 × 10–7
2 4.18 × 10–6 1.40 × 10–6 1.64 × 10–6
3 3.26 × 10–6 2.80 × 10–6 2.56 × 10–6

i)
Deduce the order of reaction with respect to haemoglobin.

(1)

ii)

Determine the order with respect to carbon monoxide using your answer to (d)(i) and the data in the table.

Justify your answer.

(2)

iii)
Write the rate equation for this reaction using your answers to (d)(i) and (d)(ii).
(1)
iv)
Calculate the rate constant, k, for the reaction, using the data from Experiment 1 and the rate equation from (d)(iii).
Include units in your answer.

(3)

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3a2 marks

This question is about transition metals and their ions.

The shape of a complex ion formed from Cr3+ ions is shown.

q6a-9cho-al-3-june-2019-qp-edexcel-a-level-chem

i)
State the coordination number of Cr3+ in this complex ion.
(1)
ii)
State the overall charge on this complex ion.
(1)

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3b3 marks

The complex ions of transition metals have different colours in aqueous solution.

Two factors that affect the colour of the solution are the oxidation number of the central metal ion, and the ligands present.

Give examples to illustrate these factors by referring to complex ions of iron and / or copper. Include the formula and colour of each complex.

An explanation of why transition metal ions are coloured is not required.

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3c
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Tungsten wire catalyses the decomposition of ammonia.

2NH3 (g) rightwards arrowN2 (g) + 3H2 (g)

In an experiment, the following results were obtained.

Time /s Partial pressure of ammonia / kPa
0 0.350
100 0.335
200 0.319
300 0.303
400 0.287
500 0.271

i)
Plot a graph of partial pressure of ammonia against time.

(2)

q6ci-9cho-al-3-june-2019-qp-edexcel-a-level-chem

ii)
Deduce the rate equation for this reaction by using your graph in (c)(i).

Justify your answer.

(2)

iii)
Use the graph to calculate the rate constant. Include units in your answer.

(2)

iv)
Describe the stages in the catalytic decomposition of ammonia by tungsten.

(3)

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4a2 marks

Nitrogen monoxide and chlorine react together to form nitrosyl chloride. 

2 NO space left parenthesis straight g right parenthesis space plus space Cl subscript 2 space left parenthesis straight g right parenthesis space rightwards arrow space 2 NOCl space left parenthesis straight g right parenthesis space

Draw a dot-and-cross diagram for nitrosyl chloride, showing only the outer shell electrons. 

q7a-9cho-al-2-june-2019-qp-edexcel-a-level-chem

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4b
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The rate equation for the formation of nitrosyl chloride is  

Rate = k[NO]2 [Cl2]

i)
Complete the table by adding the missing values. 

Experiment [NO] / moldm-3  [Cl2] / moldm-3 Rate /moldm-3 s1
1 0.122  0.241  1.09 x 10-2
2   0.482  8.72 x 10-2
3 0.366    4.91 x 10-2

(2)

ii)
Calculate the rate constant, k, using data from Experiment 1.
Include units with your answer.  

(3)

iii)
Explain how using a catalyst increases the rate constant, k. 

(2)

iv)
The heterogeneous catalyst palladium was suggested for use in this reaction.
Explain how impurities in the gaseous reactants could make the catalyst less effective.  

(3)

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1a9 marks

Gentian violet is a purple crystalline solid used as an antifungal treatment. 

It can be synthesised from dimethylphenylamine, C6H5N(CH3)2.

The dimethylphenylamine used in the synthesis can be made by the stepwise reaction of phenylamine with chloromethane.  

Step 1  2 straight C subscript 6 straight H subscript 5 NH subscript 2 space plus space CH subscript 3 Cl space rightwards arrow space straight C subscript 6 straight H subscript 5 NH left parenthesis CH subscript 3 right parenthesis space plus space straight C subscript 6 straight H subscript 5 NH subscript 3 superscript plus Cl to the power of minus

   Step 2   2 straight C subscript 6 straight H subscript 5 NH open parentheses CH subscript 3 close parentheses space plus space CH subscript 3 Cl space rightwards arrow space straight C subscript 6 straight H subscript 5 straight N left parenthesis CH subscript 3 right parenthesis subscript 2 space plus space straight C subscript 6 straight H subscript 5 NH subscript 2 superscript plus open parentheses CH subscript 3 close parentheses Cl to the power of minus

The reaction mechanism for Step 1 between phenylamine and chloromethane is the same as that in the reaction between ammonia and chloromethane.  

i)
What is the reaction type and mechanism in Step 1? 
(1)
  ☐ A electrophilic addition 
  ☐ B electrophilic substitution 
  ☐ C nucleophilic addition  
  ☐ D nucleophilic substitution  


ii)
Draw the mechanism for the reaction in Step 1.
Include curly arrows, and relevant lone pairs and dipoles. 
(4)
iii)
Describe, in outline, how a sample of a solid, such as gentian violet, is purified by recrystallisation.
Specific details of the solvent used are not required.  
(4)

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1b
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The rate constant for the reaction between a solution of gentian violet and aqueous sodium hydroxide was determined at different temperatures.

Temperature (T)
/K  		 1/ Temparature (1/T) /K-1 Rate constant, k
 / dm3 mol-1 s-1		 In k 
283.5   3.53 x 10-3 2.71 x 10-3 —5.91  
287.5   3.48 x 10-3 3.55 x 10-3  
291.5     4.75 x 10-3 —5.35 
295.0  3.39 x 10-3 6.10 x 10-3 —5.10 
298.5   3.35 x 10-3  7.60 x 10-3 —4.88 


i)
Complete the data in the table. 
(1)
ii)
Plot a graph and use it to determine the activation energy for the reaction in kJ mol-1.

You should include the value and units of the gradient of the line.

The Arrhenius equation can be shown as  

In italic space k space equals space minus E subscript straight a over straight R space cross times space 1 over T space plus space constant
(6)
q8bii-9cho-al-2-june-2019-qp-edexcel-a-level-chemGradient  
..................................................................................................
Activation energy
..................................................................................................

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2a6 marks

This question is about the effect of temperature on the rate of decomposition of
nitrogen(V) oxide.

2N2O5 (g) → 2N2O4 (g) + O2 (g)

The diagram shows the Maxwell-Boltzmann distribution of molecular energies for nitrogen(V) oxide at a temperature T1.

Ea is the activation energy of this reaction.

q9a-9cho-al-2-nov-2020-qp-edexcel-a-level-chem

i)
Give the label for the vertical axis.

(1)

ii)
Draw a second curve on the same set of axes for the same gas at a lower temperature, T2.

(2)

iii)
Explain, in terms of collisions and energy, why lowering the temperature decreases the rate of reaction.

(2)

iv)
A catalyst is added to the gas.
Label the diagram above with the symbol Ecat to show a possible activation energy for the reaction in the presence of a catalyst.

(1)

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2b5 marks

The rate constant for the decomposition of nitrogen(V) oxide was determined at two temperatures.

Temperature / K Rate constant / s−1
328 1.50×10−3
338 4.87×10−3

Calculate the activation energy for this reaction.

Include units and give your answer to an appropriate number of significant figures.

You should not attempt to use any graphical method to answer this question.

The Arrhenius equation relating two rate constants, k1 and k2 , at two different temperatures, T1 and T2 , can be expressed as

l n space open parentheses k subscript 2 over k subscript 1 close parentheses equals negative E subscript a over R open parentheses 1 over T subscript 2 minus 1 over T subscript 1 close parentheses

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3a1 mark

This question is about the reaction kinetics of an ‘iodine clock’ reaction.

One example of an ‘iodine clock’ reaction that involves the iodate(V) ions and iodide ions in acidic solution is

IO subscript 3 superscript minus space space open parentheses aq close parentheses space plus space 5 straight I to the power of minus space open parentheses aq close parentheses space plus space 6 straight H to the power of plus space open parentheses aq close parentheses space rightwards arrow 3 straight I subscript 2 space open parentheses aq close parentheses space plus space 3 straight H subscript 2 straight O space open parentheses straight l close parentheses

State why the order of reaction with respect to iodide ions cannot be five, even though 5 mol of iodide ions are shown in the equation.

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3b
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A series of experiments was carried out by a student to determine the order of reaction with respect to iodate(V) ions. The concentrations of the iodide ions and the acid were in large excess and the volume of the iodate(V) solution was varied.
The total volume of the reaction mixture was kept constant by the addition of suitable volumes of deionised water.
The following results were obtained:

Experiment Number 1 2 3 4 5 6
Volume of iodate(V) solution / cm3 10.0 7.0 5.0 3.0 2.0 1.0
Time (t) / s 180 260 357 606 900 800

(1000/t) / s-1

 5.56       1.11 1.25

i)
In experiment 6, the student forgot to add deionised water to keep the total volume the same for each experiment.
State why the total volume should be kept the same.

(1)

ii)
Complete the table and use the results from experiments 1, 2, 3, 4 and 5 to plot a graph of 1000/t against volume of iodate(V) ions.

(4)

q9bii-9cho-al-2-june-2018-qp-edexcel-a-level-chem

iii)
Deduce the order of reaction with respect to the iodate(V) ions. Justify your answer.

(2)

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3c
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A different version of the ‘iodine clock’ reaction involves mixing hydrogen peroxide with aqueous solutions of potassium iodide, sodium thiosulfate and starch.

The main reaction is

H2O2 (aq) + 2I-( aq) + 2H+ (aq) → I2 (aq) + 2H2O (l)

The reaction is first order with respect to hydrogen peroxide and iodide ions but zero order with respect to hydrogen ions.

i)
In one experiment, the following data were obtained:

Reactants Initial concentration/mol dm-3
H2O2 (aq) 1.50 × 10-3
I- (aq) 2.10 × 10-3
H+ (aq) 2.10 × 10-3

Initial rate = 1.24 × 10-3 mol dm-3 s-1

Write the rate equation and hence deduce the value of the rate constant, k, from these data. Include units and give your answer to an appropriate number of significant figures.

(2)

ii)
Explain the purpose of the starch present in the reaction mixture when starch is neither in the rate equation, nor in the reaction equation.

(2)

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3d
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Another ‘iodine clock’ reaction produced data that enabled the following graph of ln k against 1/T to be drawn.

q9d-9cho-al-2-june-2018-qp-edexcel-a-level-chem

i)
The Arrhenius equation can be expressed as

In k equals negative E subscript straight a over R cross times open square brackets 1 over T close square brackets space plus space constant

From the gradient of the graph, determine the activation energy, Ea , for this reaction.

Include a sign and units in your answer.

(3)

ii)
Give a reason for the point at ln k = −7 not being included in the line drawn on the graph.

(1)

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4a2 marks

A series of experiments was carried out to determine the kinetics of the reaction between a chloroalkane, RCl, and potassium hydroxide in aqueous solution.
A large excess of the chloroalkane was used.

The data obtained are shown.

[OH−] / mol dm−3 Time / s
0.00100 39
0.00200 31
0.00300 23
0.00400 16
0.00500 8

Plot a graph of the concentration of the hydroxide ions against time.

q11a-9cho-al-2-oct-2021-edexcel-a-level-chem

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4b2 marks

State the order with respect to hydroxide ions.
Justify your answer by reference to your graph in (a).

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4c2 marks

Deduce the type of mechanism occurring.
Justify your answer.

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4d1 mark

Give the classification of the chloroalkane in this reaction.

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5a1 mark

A bromoalkane, RBr, reacts with aqueous hydroxide ions in a nucleophilic substitution reaction.

RBr + OH− → R━OH + Br−

This reaction is first order with respect to the bromoalkane and the rate equation is

rate = k[RBr]1 [OH−]x

where x is the order of the reaction with respect to hydroxide ions.
In an experiment, a sample of the bromoalkane was added to a large excess of aqueous sodium hydroxide and the concentration of the bromoalkane was determined at regular time intervals.

Results

Time / s [RBr] / mol dm–3
0 0.100
30 0.065
60 0.042
90 0.028
120 0.019
150 0.014

This experiment is carried out using the bromoalkane dissolved in ethanol and the hydroxide ions dissolved in water.

Give a reason why a solution of hydroxide ions dissolved in pure ethanol should not be used.

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5b3 marks

Plot a graph of [RBr] against time.

q6b-9cho-al-2-nov-2020-qp-edexcel-a-level-chem

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5c
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Explain how the graph shows that the reaction is first order with respect to RBr.
Include the values of two consecutive half-lives.

You must show your working for the half-lives on the graph.

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5d4 marks

The experiment was repeated using equal concentrations of RBr and varying the concentration of hydroxide ions.

A graph was plotted of the results.

q6d-9cho-al-2-nov-2020-qp-edexcel-a-level-chem

i)
Deduce the value of x in the rate equation.

rate = k[RBr]1[OH−]x

(1)

ii)
Give the mechanism for the reaction that is consistent with the orders of reaction with respect to R━Br and hydroxide ions.
Include curly arrows and relevant lone pairs.

(3)

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5e3 marks

2-bromobutane can react with aqueous hydroxide ions by an SN1 mechanism.

Explain why the butan-2-ol produced from a single optical isomer of 2-bromobutane, using this mechanism, is not optically active.

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