CIE A Level Chemistry

Topic Questions

A LevelChemistryCIETopic Questions5. Physical Chemistry (A Level Only)5.6 Reaction Kinetics (A Level Only)

Syllabus Edition

First teaching 2020

Last exams 2024

|

5.6 Reaction Kinetics (A Level Only)

DownloadView
Easy
Medium
Hard
Easy
Medium
Hard
1a3 marks

The rate equation for the reaction between reactants X, Y and Z is shown below.

rate = k [X]2 [Y]

State the orders with respect to X, Y and Z.

How did you do?

1b1 mark

State the overall order of this reaction.

How did you do?

1c
Sme Calculator3 marks

The rate of reaction is 3.72 x 10-5 mol dm-3 s-1 when the

  • concentration of X is 0.01 mol dm-3
  • concentration of Y is 0.02 mol dm-3
  • concentration of Z is 0.04 mol dm-3

Calculate the rate constant, k, for this reaction, including the units.

How did you do?

1d
Sme Calculator2 marks

The experiment was repeated but the initial concentration of X was doubled, all other concentrations remained the same.

State what the effect would be on the rate of reaction.

Explain your answer.

How did you do?

Did this page help you?

2a1 mark

Bromide ions and bromate(V) ions react in acidic conditions to form aqueous bromine in the following equation.

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

A series of experiments was carried out at a given temperature to find the rate equation for the reaction.

The results from experiments using different hydrogen ion concentrations are shown in Fig. 2.1.

reaction-rate-h

Fig. 2.1

Use the information in Fig. 2.1 to determine the order of reaction with respect to hydrogen ions.

How did you do?

2b1 mark

Experiments using different bromide concentrations showed that the order of reaction with respect to bromide ions was first order. 

On the graph in Fig. 2.2, sketch a graph to show how the concentration of bromide ions would change during the course of a reaction.

conc-time-graph-br--blank


Fig. 2.2

How did you do?

2c2 marks

Overall, the reaction between bromide ions and bromate(V) ions in acidic conditions is fourth order.

i)
Deduce the order with respect to bromate(V) ions.

ii)
Using your answer to part (a) and the information in part (b), write the rate equation for the reaction.

How did you do?

2d2 marks

Bromide ions and bromate(V) ions react in acidic conditions to form aqueous bromine in the following equation.

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

i)
Using your answer to part (c), write an expression for the rate constant for the reaction between bromide ions and bromate(V) ions in acidic conditions.

ii)
Suggest suitable units for the rate constant.

How did you do?

Did this page help you?

3a1 mark

Hydrogen peroxide, H2O2, is a colourless liquid. It is widely used in cosmetic and medical products. It is an effective disinfectant and bleaching agent.

Hydrogen peroxide is unstable and will decompose slowly to form water and oxygen. The rate of decomposition can be increased using manganese(IV) oxide as a catalyst.



2H2O2 (aq) → 2H2O (l) + O2 (g)

The graph in Fig. 3.1 shows how hydrogen peroxide decomposes in the presence of manganese(IV) oxide.

5-1_q3a-ocr-a-as--a-level-easy-sq

Fig. 3.1 

State what is meant by the half-life of a reaction.

How did you do?

3b
Sme Calculator3 marks

Use the graph in Fig. 3.1 to show that this reaction is first order with respect to hydrogen peroxide. 

Deduce the rate equation of the reaction.

How did you do?

3c
Sme Calculator4 marks

Using the graph in Fig. 3.2, determine

i)
the rate of reaction, in mol dm-3 s-1, at 100 seconds.

ii)
the rate constant for this reaction. State the units.

Your answer must show full working on the graph in Fig 3.2.

5-1_q3a-ocr-a-as--a-level-easy-sq

Fig. 3.2

How did you do?

3d1 mark

When the initial concentration of hydrogen peroxide was halved, state what the effect, if any, on the half-life of this reaction would be.

How did you do?

Did this page help you?

1a
Sme Calculator4 marks

In the presence of acid, H+(aq), chlorine and propanone react together:

CH3COCH3 (aq) + Cl2 (aq) → CH3COCH2Cl (aq) + HCl (aq)

A student carried out an investigation into the kinetics of this reaction.

The student investigated how different concentrations of chlorine affect the initial rate of the reaction. A graph of [Cl2 (aq)] against time is shown in Fig. 1.1.

5-1_q1a-ocr-a-as--a-level-hard-sq

FIg. 1.1

The student then investigated how different concentrations of propanone and H+(aq) affect the initial rate of reaction.

Their results are shown below.

Experiment  [Cl2 (aq)]
/ mol dm-3		  [CH3COCH3 (aq)]
/ mol dm-3		  [H+(aq)]
/ mol dm-3		 Inital rate
/ mol dm-3 s-1
1 0.003 0.75 0.05 0.18 x 10-5
2 0.003 1.50 0.15 1.08 x 10-5
3 0.003 1.50 0.30 2.16 x 10-5

a)
Use the student's results to determine the reaction orders. Explain your answer.

How did you do?

1b
Sme Calculator4 marks

Deduce the rate equation and calculate the rate constant for this reaction, including the units.

Rate equation ...........................................................




k = ................... 
units = ................................. 

How did you do?

1c
Sme Calculator1 mark

The student varied the concentrations of the reactants in another experiment and they found the rate to be 0.26 x 10-5 mol dm-3 s-1. They also used a pH probe and found that the reaction mixture had a pH of 2.

Calculate the initial rate of the reaction mixture if the amount of acid added was altered to give a pH of 1.

Assume the temperature and the initial concentrations of the other reactants remained the same.





Initial rate = ..................................

How did you do?

1d2 marks

The experiment was repeated at a lower temperature. State what the effect would be of this change, if any, on the rate and the rate constant of the reaction.

How did you do?

Did this page help you?

2a1 mark

Nitrogen monoxide, NO, reacts with oxygen, O2. The rate equation for this reaction is shown below.

rate = k[NO(g)]2[O2(g)]

State what would happen to the rate of the reaction if the initial concentration of NO is tripled and the initial concentration of O2 is halved.

How did you do?

2b2 marks

Nitrogen monoxide is produced by combustion in car engines and released into the atmosphere. 

In the lower atmosphere, nitrogen monoxide is responsible for the formation of ozone in a series of reactions shown below.

NO (g) + ½O2 (g) → NO2 (g)

NO2 (g) → NO (g) + O (g)

O2 (g) + O (g) → O3 (g)

i)
What is the overall equation for this series of reactions?
[1]
ii)
Explain why NO is acting as a homogenous catalyst in this reaction.

[2]

How did you do?

2c3 marks

When nitrogen monoxide is present in the upper atmosphere, is it involved in the removal of ozone, O3. The overall equation for the reaction is shown below.

O (g) + O3 (g) → 2O2 (g)

The rate equation is:   rate = k[NO(g)][O3(g)]

i)
State how this shows that the mechanism contains more than one step.

[1]
ii)
Deduce a possible two-step mechanism for this reaction.

[2]

How did you do?

2d2 marks

Ozone in the lower atmosphere can react with ethene to produce methanal, CH2O (g) which contributes to low-level smog. The equation is shown below.

O3 (g) + C2H4 (g) → 2CH2O (g) + ½O2 (g)

The order of the reaction with respect to both reactants is first order. The initial rate of formation of methanal was found to be 2.0 x 10-11 mol dm-3 s-1.

The initial concentration of ozone was doubled and the initial concentration of ethene was tripled.

Calculate the initial rate of oxygen formation.

How did you do?

Did this page help you?

3a
Sme Calculator3 marks

Bromate(V) ions and bromide ions react in the presence of acid to form bromine and water.

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

A  student carried out a series of experiments to investigate how the rate of the reaction of bromate and bromide in the presence of an acid varies with temperature.

The time taken, t, was measured for a fixed amount of bromine to form at different temperatures. The results are shown in the Table 3.1.

Table 3.1

Temperature (T ) / K bold 1 over bold T bold space bold cross times bold space bold 10 to the power of bold minus bold 3 end exponent / K-1 Time (t ) / s begin mathsize 14px style bold 1 over bold t end style / s-1 ln bold 1 over bold t
408 2.451 21.14 0.0473 -3.051
428   10.57 0.0946 -2.358
448 2.232 5.54    
468 2.137     -1.106
488 2.049 1.71 0.5851 -0.536

Calculate the missing values to complete the table above.

How did you do?

3b4 marks

The relationship between the rate constant, k, and the activation energy, Ea, and temperature, T is given by the following equation.

ln k = ln A + begin mathsize 14px style fraction numerator negative E subscript straight a over denominator R T end fraction end style

In this experiment, the rate constant, k, is directly proportional to begin mathsize 14px style 1 over t end style. Therefore, 

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

Use your answers from part (a) to plot a graph of ln 1 over t against begin mathsize 14px style 1 over T end style x 10-3 on the graph in Fig. 3.1.

q4c_rate-equations_structured_hard_a_level_aqa_chemistry-2

Fig. 3.1

How did you do?

3c
Sme Calculator4 marks

Use your graph in Fig. 3.1 and information from part (c) to calculate a value for the activation energy, in kJ mol–1, for this reaction. Show your working. 

The value of the gas constant, R = 8.31 J K–1 mol–1




Ea = ....................... kJ mol-1

How did you do?

Did this page help you?

1a
Sme Calculator5 marks

The initial rate of the reaction of chlorine dioxide, ClO2, and fluorine, F2, is measured in a series of experiments at a constant temperature.

2 ClO2 + F2 → 2ClO2F

The results obtained are shown in Table 1.1.

Table 1.1

experiment [ClO2] / mol dm–3 [F2] / mol dm–3 initial rate / mol dm–3 s–1
1 0.010 0.060 2.20 × 10–3
2 0.025 0.060 to be calculated
3 to be calculated 0.040 7.04 × 10–3

The rate equation is rate = k[ClO2][F2].

i)
Explain what is meant by order of reaction with respect to a particular reagent.

 [1]

ii)
Use the results of experiment 1 to calculate the rate constant, k, for this reaction. Include the units of k.

k = ............................. units ............................. [2]

iii)
Use the data in Table 1.1 to calculate the initial rate in experiment 2.

initial rate = ...................................... mol dm–3 s–1 [1]

iv)
Use the data in Table 1.1 to calculate [ClO2] in experiment 3.

[ClO2] = ............................................ mol dm–3 [1]

How did you do?

1b3 marks
i)
Explain what is meant by rate-determining step.

 [1]

ii)
The mechanism of the reaction between ClO2 and F2 has two steps.

Suggest equations for the two steps of this mechanism.

step 1 ..............................................................................

step 2 ...............................................................................

[1]

iii)
State and explain which of the two steps is the rate-determining step.

rate-determining step = ..........................
[1]

How did you do?

1c1 mark

Describe the effect of temperature change on the rate of a reaction and the rate constant.

How did you do?

Did this page help you?

2a
Sme Calculator4 marks

This question is about the reactions of different unknown compounds.

Two compounds, X and Y, were reacted together. 

 

The initial rate of reaction was measured when compound X and compound Y were reacted together. The temperature was kept constant and the results of the experiments are shown in Table 2.1.

 
Table 2.1
 

experiment

[X] / mol dm-3

[Y] / mol dm-3

rate of reaction
/ mol dm-3 s-1

1

0.030

0.040

4.0 x 10-4

2

0.045

0.040

6.0 x 10-4

3

0.045

0.060

9.0 x 10-4

4

0.060

0.120

2.4 × 10-3
  
i)
Use the data in Table 2.1 to deduce the order of reaction with respect to X.
 
[1]
 
ii)
State the order of the reaction with respect to Y.
 
[1]
 
iii)
Determine the overall order of the reaction.
 
[1]
 
iv)
Write the rate equation for the reaction.
 
[1]

How did you do?

2b
Sme Calculator6 marks

Three separate experiments were carried out at 400K with different starting concentrations of A and B. The results are shown in Table 2.2.

 
Table 2.2
 

experiment 

[A] / mol dm-3

[B] / mol dm-3

rate of reaction
/ mol dm-3 s-1

1

0.50

0.30

7.6 x 10-4

2

0.25

0.30

1.9 x 10-4

3

0.25

0.60

3.8 x 10-3
 
i)
Deduce the order of reaction with respect to each reactant. Explain your reasoning.
 
order with respect to [A] ..............................................................................................
 
order with respect to [B] ................................................................................................
 
[2]
 
ii)
State the rate equation for this reaction. Use the rate equation to calculate the rate constant.
 
Include the units for the rate constant in your answer.
 
rate =
 
rate constant, k = ..............................
 
units of k = ..............................
 
[4]

How did you do?

2c
Sme Calculator2 marks

The overall rate equation for a reaction is rate = k[P]2[Q]

 
i)
State what the units would be of the rate constant, k, in this reaction.
 
[1]
 
ii)
State the overall order of the reaction above.
 
[1]

How did you do?

2d
Sme Calculator2 marks

Chemists measured the rate of a chemical reaction in a series of experiments between compounds C and D at a fixed temperature as shown in Table 2.3.

 
Table 2.3
 

experiment

[C] / mol dm-3

[D] / mol dm-3

rate of reaction
/ mol dm-3 s-1

1

0.13

0.12

0.32 x 10-3

2

0.39

0.12

2.88 x 10-3

3

0.78

0.24

11.52 x 10-3
 

Dedude the order of reaction with respect to

  • C ..................................................
  • D ..................................................

and write the overall rate equation for this reaction.

 

How did you do?

Did this page help you?

3a
Sme Calculator4 marks

The initial rate of reaction for iodine and propanone in acid solution is measured in a series of experiments at constant temperature.

CH3COCH3 + I2 rightwards arrow with straight H to the power of plus on top CH3COCH2I + HI

The rate equation was determined experimentally to be as shown.

rate = k [CH3COCH3][H+]

i)
State the order of reaction with respect to
  • CH3COCH3 ..................................................
  • I2 ..................................................
  • H+ ..................................................
and state the overall order of the reaction. ..................................................
 
[2]
 
ii)
Explain the role of the acid.
 
[2]

How did you do?

3b
Sme Calculator3 marks

The rate of this reaction is 5.40 × 10–3 mol dm–3 s–1 when

  • the concentration of CH3COCH3 is 1.50 × 10–2 mol dm–3
  • the concentration of I2 is 1.25 × 10–2 mol dm–3
  • the concentration of H+ is 7.75 × 10–1 mol dm–3.

i)
Calculate the rate constant, k, for this reaction. State the units of k.
 
k = ..............................
 
units = ..............................
 
[2]
 
ii)
Complete the table by placing one tick (✔) in each row to describe the effect of increasing the temperature on the rate constant and on the rate of reaction.
 
  decreases no change  increases
rate constant       
rate of reaction      
 
[1]

How did you do?

3c2 marks

Fig. 3.1 is produced from the results, which shows how the concentration of I2 changes during the reaction.

 
5-6-3c-m-iodine-half-life-graph
 
Fig. 3.1
 

Describe how Fig 3.1 could be used to determine the initial rate of the reaction.

How did you do?

3d1 mark

On Fig 3.2, sketch a graph to show how the initial rate changes with different initial concentrations of H+ in this reaction.

 
blank-rate-concentration-graph
 
Fig. 3.2 
 

How did you do?

Did this page help you?

4a2 marks

The equation for the decomposition of hydrogen peroxide without a catalyst is shown.

2H2O2 (aq) → 2H2O (l) + O2 (g)

With this information, a student suggests that the rate equation for this reaction is as follows.

 
rate = k [H2O2]2 
 

Explain if the student is correct. 

How did you do?

4b3 marks

A student carries out separate experiments using different initial concentrations of H2O2. The initial rate of each reaction is measured.

 

The table shows the results that are obtained.

 
[H2O2] / mol dm-3 0.100 0.210 0.285 0.420 0.540 0.700
rate / mol dm-3 s-1 0.0055 0.0116 0.0157 0.0230 0.0297 0.0385
 
i)
Plot a graph on the grid of H2O2 concentration against rate of reaction.
 
Draw a line of best fit through the plotted points. 
 
[2]
 
8qSAOUzu_5-6-4b-m-blank-rate-concentration-graph-2-a
 
ii)
State the rate equation for this reaction.
 
[1]

How did you do?

4c2 marks

Another student monitors the concentration of H2O2 over time. The graph obtained is shown.

 
5-6-4c-m-h2o2-half-life-graph
 

Using appropriate calculations, describe how the student could use this graph to prove the order of reaction with respect to H2O2. 

How did you do?

4d
Sme Calculator3 marks

Under certain conditions, the decomposition of hydrogen peroxide is found to be first order with respect to hydrogen peroxide, with a rate constant, k, of 2.0 × 10–6 s–1.

 
i)
Calculate the initial rate of decomposition of a 0.65 mol dm–3 hydrogen peroxide solution.
 
initial rate = .............................. mol dm–3 s–1
 
[1]
 
ii)
Explain the effect (if any) of decreasing the temperature on the rate constant and the rate of reaction.
 
[2]

How did you do?

Did this page help you?

5a2 marks

This question is about nitrogen oxides.

Nitrogen monoxide is produced by combustion in car engines and released into the atmosphere. 
 
In the lower atmosphere, nitrogen monoxide is responsible for the formation of ozone in a series of reactions shown below.

NO (g) + ½O2 (g) → NO2 (g)

NO2 (g) → NO (g) + O (g)

O2 (g) + O (g) → O3 (g)

i)
What is the overall equation for this series of reactions?
 
[1]
  
ii)
Explain why NO is acting as a catalyst in this reaction.
 
[1]

How did you do?

5b
Sme Calculator2 marks

The rate equation for the reaction between nitrogen monoxide (NO) and oxygen (O2) under certain conditions is given.

 
Rate = k [NO]2[O2]
 

The result of an experiment in which NO reacted with O2 is shown in the table. 

 

initial [NO] / mol dm-3

initial [O2] / mol dm-3

initial rate of reaction 
/ mol dm-3 s-1

5.0 x 10-2

1.0 x 10-2

6.5 x 10-4
  

Use the data and the rate equation to calculate a value for the rate constant k.

Give the units of k.

How did you do?

5c
Sme Calculator4 marks

Nitrogen dioxide reacts with carbon monoxide at 100 ℃ to form nitrogen monoxide and carbon dioxide.

 
2NO2 (g) + CO (g) → NO (g) + CO2 (g)

 

The rate of this reaction was measured at different initial concentrations of the two reagents.

 

The rate equation was determined to be

 

Rate = k [NO2]2 
 

The table shows an incomplete set of results.

 

experiment

[NO2] / mol dm-3

[CO] / mol dm-3

Initial rate 
/ mol dm-3 s-1

1

4.1 x 10-2

2.8  x 10-3

3.3  x 10-5

2

7.8  x 10-3

2.8  x 10-3

 to be calculated

3

 to be calculated

5.6  x 10-3

1.8  x 10-4
 
i)
Use the data from Experiment 1 to calculate a value for the rate constant, k, at this temperature. State its units.
 
[2]
 
ii)
Use your value of k from (i) to complete the table for the reaction between NO2 and CO. 
 
[2]

How did you do?

5d2 marks

Nitrogen monoxide, NO (g), reacts with hydrogen, H2 (g), under certain conditions.

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

The rate equation for this reaction is given.

 
rate = k [NO]2 [H2]
 

One proposed mechanism for this reaction occurs in two steps.

  1. 2NO + H2 → N2 + H2O2 
  2. H2O2 + H2 → 2H2O

 

Explain which of the steps is the rate-determining step.

How did you do?

Did this page help you?