CIE AS Chemistry

Topic Questions

ASChemistryCIETopic Questions1. Physical Chemistry1.8 Reaction Kinetics

Syllabus Edition

First teaching 2020

Last exams 2024

|

1.8 Reaction Kinetics

DownloadView
Easy
Medium
Hard
Easy
Medium
Hard
1a2 marks

This question is about effective reactions and reaction rates. 

According to collision theory, state two conditions that particles need for an effective collision to occur.

How did you do?

1b1 mark

An increase in concentration means that there are more particles per unit volume.

In terms of collisions, explain how this increases the rate of reaction. 

How did you do?

1c
Sme Calculator2 marks

Aqueous hydrogen peroxide, H2O2, decomposes to form oxygen and water.

2H2O2 (aq) → 2H2O (l) + O2 (g)

A student investigates the decomposition of a hydrogen peroxide solution as outlined below.

  • The student adds 25.00 cm3 of H2O2 (aq) to a conical flask.
  • The student adds a small spatula measure of manganese dioxide, MnO2.
  • They quickly connect the flask to a gas syringe.
  • The student measures the volume of oxygen every 100 seconds.
i)
State the role of the manganese dioxide in this reaction.
[1]
The student obtained the following results.

 

Time / s 0 100 200 300 400 500 600 700
Volume of O2 / cm3 0.0 7.0 13.5 18.0 21.0 22.5 23.0 23.0
 
ii)
Calculate the average rate of reaction, in cm3 s-1, for the first 100 seconds of the reaction.
[1]

How did you do?

1d
Sme Calculator3 marks

The student plotted a graph of volume of O2 against time.

 
1-8-1d-e-volume-of-o2-vs-time
 

Use the student's graph and tangent to find the rate of the reaction, in cm3 s–1, at t = 300 s.

Show your working. 

How did you do?

Did this page help you?

2a2 marks

This question is about the following general reaction

A + B ⇌ C + D

The reaction pathway diagram for the reaction is shown in Fig. 2.1.

1-8-2a-e-reaction-profile-a-and-b
 
 Fig. 2.1
 

Explain whether the forward reaction is exothermic or endothermic. 

How did you do?

2b1 mark

Define the term activation energy.

How did you do?

2c
Sme Calculator2 marks

Use Fig. 2.1 to calculate the activation energy for the forward and backward reactions.

How did you do?

2d3 marks

Explain, using Fig. 2.2, how the addition of a catalyst affects the rate of reaction.

 
3-5_q2d-ocr-a-as--a-level-easy-sq
Fig. 2.2

How did you do?

Did this page help you?

3a2 marks

This question is about Boltzmann distribution curves.

The Boltzmann distribution curve of molecular energies for a general reaction at a given temperature is shown in Fig. 3.1.

  
3-5_5a-ocr-a-as--a-level-easy-sq
Fig. 3.1
 

State what will happen to the curve when the temperature of the reaction is decreased.  

How did you do?

3b1 mark

Comment on how, if at all, the total area under a Boltzmann distribution curve changes with temperature.

How did you do?

3c2 marks

State what happens to the Boltzmann distribution curve in Fig. 3.1 when a catalyst is added to the reaction.

How did you do?

3d1 mark

The Boltzmann distribution of energies for a gas is shown in Fig. 3.2.

 
3-5_5d-ocr-a-as--a-level-easy-sq
Fig. 3.2
 

State what the shaded area of Fig. 3.2 represents. 

How did you do?

Did this page help you?

1a4 marks

Reaction rates can be affected by a range of factors including changes in pressure and temperature.

Fig 1.1

xAu0N0~R_graph

On Fig 1.1:

i)
Sketch one Maxwell-Boltzmann distribution labelled T1 and a second Maxwell-Boltzmann distribution at a higher temperature labelled T2.

[2]
ii)
State how the mean energy of the molecules would be at T2 compared to T1.

[2]

How did you do?

1b6 marks

Hydrogen iodide can be used in the manufacturing of pharmaceuticals and can be broken down back into its elements in standard form, iodine and hydrogen. 

2HI (g) → H2(g) + I2(g) ΔH = - 52 kJ mol-1

The activation energy when uncatalysed is +183 kJ mol-1 and when catalysed with gold it is +105 kJ mol-1. 

i)
Sketch a reaction profile for the reaction, including the curves for the activation energies for both the catalysed and uncatalysed reactions.

ii)
Calculate the activation energy for the reverse reaction in both the uncatalysed and catalysed reactions.

iii)
Explain why increasing the concentration of hydrogen iodide gas results in a faster reaction rate.

How did you do?

1c3 marks

Catalysts are often used in industrial processes and can be used in a variety of forms. 

 

i)
Explain why it is likely that the solid gold catalyst was used in powder form to catalyse the reaction mentioned in part (c). 
[1]
ii)
Gold is a heterogeneous catalyst used in the formation of hydrogen iodide. State the difference between a homogenous and heterogenous catalyst.

[1]

iii)
State how, if at all, the area under the curve of a Maxwell-Boltzmann distribution curve, changes as a catalyst is introduced without changing the temperature or the total number of molecules.
[1]

How did you do?

1d3 marks

The Contact process is an important industrial process, contributing to the production of sulfuric acid. In the Contact process, solid vanadium (V) oxide, a heterogeneous catalyst, is used to make sulfur trioxide from sulfur dioxide and oxygen. This process is reversible.

i)
Write a balanced symbol equation for this reaction. Include state symbols in your answer.
[1]
ii)
Explain why the use of the catalyst in the Contact process, reduces energy demand and benefits the environment.
[2]

How did you do?

Did this page help you?

2a
Sme Calculator5 marks

0.5 g of magnesium reacts with 50 cm3 of 0.01 moldm-3 nitric acid. Magnesium is in excess.

A graph monitoring the volume of hydrogen gas produced is shown below:

6-1-ib-sl-sq-hard-q3a-rate-of-reaction-graph
i)
Calculate the mean rate of reaction over the first 15 seconds of the reaction
[1]
ii)
Calculate the actual rate of reaction at 15 seconds
[3]
iii)
Explain the difference in values for rate
[1]

How did you do?

2b3 marks

Compare the expected rate and progress of the reaction if 25 cm3 of 0.2 mol dm-3 nitric acid was used instead of 50 cm3 of 0.1 mol dm-3 nitric acid.

How did you do?

2c2 marks

Suggest one change to the reaction that could be made to produce more hydrogen gas in total and explain your choice.

How did you do?

2d2 marks

Suggest why it is often better to study a slower reaction instead of a faster one.

How did you do?

Did this page help you?

3a4 marks

A Maxwell-Boltzmann distribution curve is shown below in Fig 3.1 

1-8-3a-h-q3a-botlzman-distribution-curve

Fig 3.1

For the changes detailed in part (i) and (ii) state and explain the effect the change would have on:

  • The area under the curve 
  • The value of the most probable energy of the molecules, Emp
  • The proportion of molecules with greater than or equal to Ea 
i)
The temperature of the original reaction is increased, but no other changes are made.
[2]
ii)
A catalyst is added to the original reaction mixture, but no other changes are made.
[2]

How did you do?

3b4 marks

A chemist performed a reaction at three different temperatures, 100 K, 300 K and 700 K as shown by the Maxwell-Boltzmann distribution graph in Fig 3.2.

Fig 3.2

maxwell-boltzman-three-diff-temps

Fig 3.2

i)
Label each curve in Fig 3.2 ith the correct temperature values, 100 K, 300 K and 700 K.
[1]

 

ii)
Consider the following statement, ‘All reacting molecules have higher kinetic energy at 700 K than they do at 300 K’.

State whether you agree this statement is correct and justify your reasons.
[3]

How did you do?

3c5 marks

Hydrogen will react with chlorine to form the hydrogen halide, hydrogen chloride, a colourless gas.

H2 (g) + Cl2 (g) → 2HCl (g)

i)
Give one reason why most collisions between hydrogen and chlorine molecules do not lead to the formation of hydrogen chloride. 

[1]

ii)
Apart from changing the temperature, state and explain two ways of speeding up the formation of hydrogen chloride.
[4]

How did you do?

Did this page help you?

1a3 marks

Fig. 1.1 below shows, for a given temperature T, a Boltzmann distribution of the kinetic energy of the molecules of a mixture of two gases that will react together.


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

1-8m-q1-boltzmann

Fig. 1.1

On Fig. 1.1 above,

i)
draw a new distribution curve, clearly labelled T2, for the same mixture of gases at a lower temperature, T2.

[2]
ii)
mark clearly, as H, the position of the activation energy of the reaction at the lower temperature, T2.

[1]

How did you do?

1b2 marks

Explain the meaning of the term activation energy.

How did you do?

1c2 marks
i)
On the energy axis in Fig. 1.1, mark the position, clearly labelled C, of the activation energy of the reaction when a catalyst is used.

[1]

ii)
Use your answer to (i) to explain how the use of a catalyst results in reactions occurring at a faster rate.

 

[1]

How did you do?

1d4 marks

Two reactions involving aqueous NaOH are given below.

CH3CHBrCH3 + NaOH → CH3CH(OH)CH3 + NaBr reaction 1
H2SO4 + 2NaOH → Na2SO4 + 2H2O reaction 2

The reagents in reaction 1 must be heated together for some time for the reaction to occur.
Whereas, reaction 2 is almost instantaneous at room temperature.

Suggest brief explanations why the rates of these two reactions are very different.

How did you do?

Did this page help you?

2a2 marks

A platinum-rhodium catalyst used in the reaction forming nitrogen(II) oxide from ammonia.

4NH3 (g) + 5O2 (g) ⇌ 4NO (g) + 6H2O (g)

i)

State what is meant by the term heterogeneous catalyst.

[1]

ii)

Explain why a catalyst has no effect on the yield of the products in the reaction.

[1]

How did you do?

2b3 marks

A group of students were completing a practical, investigating the factors which affect the rate of the following chemical reaction. 

A (s) + B (aq) → C (g)

The students collected the gas produced and plotted the graph shown in Fig. 1.1. 

gas-volume-evolved-over-time

Fig. 1.1

i)

State and explain what the letter R represents on the student's graph.

[1]

ii)

In the original reaction above, the students used 0.5 g of A and 50 cm3 of 1.0 mol dm-3 of B. Sketch a curve on the graph in Fig 1.1 to show how the total volume of gas collected would change if the students still used 0.5 g of A, but used 50 cm3 of 2.0 mol dm-3 of B.

[2]

How did you do?

2c2 marks

Explain why the gradient of the curve in part (b) decreases as the time of the reaction progresses.

How did you do?

2d2 marks

Another way to increase the rate of reaction is to increase the temperature. 

Explain why a small increase in temperature has a large effect on the initial rate of a chemical reaction.

How did you do?

Did this page help you?

3a3 marks

This question is about how different factors affect the rate of a chemical reaction.

A reaction between reactant molecules can only occur when collisions between the reactant molecules are effective.

i)
Explain what is meant by the term effective collision.


[1]

ii)
State two factors that could cause an ineffective collision.


[2]

How did you do?

3b5 marks

A student made the following statement about factors that affect the rate of a chemical reaction.

'The rate of a reaction increases with temperature as there are more collisions'

Discuss why this statement is only true to an extent and what other factors need to be considered to fully explain how the rate of a reaction is affected by temperature.

How did you do?

3c2 marks

Hydrogen and oxygen can react to form water in an exothermic reaction.

2H2 (g) + O2 (g) → 2H2O (g)

The rate of this reaction depends on the pressure as well as the temperature.

Describe and explain the effect of increasing the pressure on this reaction.

How did you do?

3d2 marks

If the rate of reaction increases suddenly, an explosion can occur.

A highly exothermic reaction, such as the reaction in (c), is at more risk of exploding than a less exothermic reaction.

Suggest why.

How did you do?

Did this page help you?

4a2 marks

A series of experiments was carried out to investigate the factors which affect the rate of reaction between calcium carbonate and dilute hydrochloric acid.

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

  • 50.0 cm3 of hydrochloric acid was added to 10 g of small pieces of calcium carbonate (an excess) in a conical flask placed on an electronic balance.
  • The loss in mass of the flask and its contents was recorded every 30 seconds for 10 minutes.
  • The experiment was repeated using a different concentration of hydrochloric acid or a different temperature.
  • The results are shown in Table 1.1

Table 1.1

Experiment

Concentration of hydrochloric acid
/ mol dm−3

 Temperature / °C
1 0.50 20
2 0.50 60
3 1.00 20

The results of Experiment 1 are shown in Fig. 1.1.

q4-9cho-al-3-oct-2021-edexcel-a-level-chem

Fig. 1.1

Draw curves on the graph in Fig 1.1 to show the results you would expect for Experiments 2 and 3.

Label the curves 2 and 3.

How did you do?

4b
Sme Calculator3 marks

Determine the initial rate of reaction for Experiment 1.

You must show your working on the graph in Fig 1.2.
Include units in your answer.

q4b-9cho-al-3-oct-2021-edexcel-a-level-chem
Fig 1.2
 
Initial rate of reaction .........................................................

How did you do?

4c
Sme Calculator1 mark

Calculate the average rate of reaction over the first 240 seconds of Experiment 1.



Average rate of reaction....................................................................

How did you do?

4d2 marks

The student repeated each experiment but used 10.0 g of larger sized pieces of calcium carbonate.

Suggest what effect this would have on the rate of reaction. Give your reasoning.

How did you do?

Did this page help you?

5a4 marks

Ammonia can be produced by the reaction of nitrogen and hydrogen.

N2 (g) + 3H2 (g) rightwards harpoon over leftwards harpoon 2NH3 (g)          ΔH = -92 kJ mol-1

The reaction can be catalysed and the activation energy for this catalysed reaction is +109 kJ mol-1

Complete the reaction pathway diagram in Fig. 1.1 for the uncatalysed and the catalysed reaction between nitrogen and hydrogen.

You should label the following:

  • products
  • the enthalpy change of reaction, ΔH
  • the activation energy of the forward, uncatalysed reaction, Ea
  • the activation energy of the forward, catalysed reaction, Ec

1-8-reaction-kinetics-5a-a

Fig. 1.1

How did you do?

5b
Sme Calculator1 mark

Calculate the value of the activation energy of the catalysed decomposition of ammonia into nitrogen and hydrogen.

Show your working.

activation energy .............................................. kJ mol-1

How did you do?

5c1 mark

Catalysts, such as iron used in the production of ammonia, increase the rate of reaction.

Explain why. Use a labelled Boltzmann distribution to explain your answer.

How did you do?

5d3 marks

Platinum is used as a catalyst in catalytic converters which are fitted to vehicle exhaust systems to remove nitrogen oxide from the exhaust gases.

2NO (g) + 2CO (g) → N2 (g) + 2CO2 (g)

i)
State the type of catalyst that platinum is in a catalytic converter

[1]

ii)
Explain, using oxidation numbers, if nitrogen is being oxidised or reduced in this reaction.

[2]

How did you do?

Did this page help you?