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ASChemistryCIEExam Questions8. Reaction Kinetics8.1 Rate of Reaction

Rate of Reaction (CIE AS Chemistry)

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8.1 Rate of Reaction

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8.1 Rate of Reaction

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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.

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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. 

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1c
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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]

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1d
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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. 

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1a2 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]

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1b3 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]

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1c2 marks

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

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1d2 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.

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2a3 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]

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2b5 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.

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2c2 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.

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2d2 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.

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3a2 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 3.1

Table 3.1

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. 3.1.

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

Fig. 3.1

Draw curves on the graph in Fig 3.1 to show the results you would expect for Experiments 2 and 3.

Label the curves 2 and 3.

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3b
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Determine the initial rate of reaction for Experiment 1.

You must show your working on the graph in Fig 3.2.
Include units in your answer.

q4b-9cho-al-3-oct-2021-edexcel-a-level-chem
Fig 3.2
 
Initial rate of reaction .........................................................

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3c
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Calculate the average rate of reaction over the first 240 seconds of Experiment 1.



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

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3d2 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.

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1a
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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]

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1b3 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.

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1c2 marks

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

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1d2 marks

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

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