Effect of Catalyst on the rate of reaction

1
Effect of Catalyst on the rate of reaction

• Experiment 1.4 To study the effect of a catalyst
  on the rate of decomposition of hydrogen peroxide

2
Effect of Catalyst on the rate of reaction

• Problem statement
• How do catalyst affect the rate of decomposition
  of hydrogen peroxide

3
Effect of Catalyst on the rate of reaction

• Hypothesis
• Manganese (IV) oxide speed up the decomposition
  of hydrogen peroxide

4
Effect of Catalyst on the rate of reaction

• Variables
• (a) Manipulated variable The presence of
  manganese (IV) oxide
• (b) Responding variable The release of oxygen
  gas
• (c) Fixed (controlled) variables Volume and
  concentration of hydrogen peroxide

5
Effect of Catalyst on the rate of reaction

• Apparatus
• Boiling tube and wooden splinter
• Material
• Hydrogen peroxide and manganese (IV) oxide

6
Effect of Catalyst on the rate of reaction

• Procedure
• 1 A boiling tube is half-filled with hydrogen
  peroxide.
• 2 A glowing splinter is placed at the mouth of
  the boiling tube to test for the gas evolved
  (Figure 1.25).

7
Effect of Catalyst on the rate of reaction

• Procedure
• 3 The changes that take place inside the boiling
  tube and on the glowing splinter are recorded.
• 4 0.5 g of manganese (IV) oxide, MnO2 is added
  to hydrogen peroxide and shaken. The changes that
  take place in the boiling tube and on the glowing
  splinter are recorded.

8
Effect of Catalyst on the rate of reaction

• Results

9
Effect of Catalyst on the rate of reaction

• Discussion
• 1 Hydrogen peroxide decomposes to oxygen gas and
  water according to the equation
• 2H2O2 (aq) ? 2H2O(l) O2 (g)

10
Effect of Catalyst on the rate of reaction

• Discussion
• 2 The glowing splinter is rekindled in the
  presence of oxygen gas.

11
Effect of Catalyst on the rate of reaction

• Conclusion
• The rate of evolution of oxygen gas increases
  when manganese (IV) oxide is added to
• hydrogen peroxide. This proves that manganese
  (IV) oxide acts as a catalyst and speeds up the
  decomposition of hydrogen peroxide to water and
  oxygen. The hypothesis is accepted.

12
The effect of concentration of hydrogen peroxide
on the rate of reaction

• 1 The graph in Figure 1.21 shows the effect of
  concentration of hydrogen peroxide on the rate of
  decomposition of hydrogen peroxide.

13
The effect of concentration of hydrogen peroxide
on the rate of reaction

• In Experiment I, 50 cm3 of 0.14 mol dm-3 of
  hydrogen peroxide and 0.2 g of manganese (IV)
  oxide are used.
• In Experiment II, a solution containing 25 cm3 of
  the same hydrogen peroxide mixed with 25 cm3 of
  water and 0.2 g of manganese (IV) oxide are used.
  For both the experiments, the temperature is kept
  constant.

14
The effect of concentration of hydrogen peroxide
on the rate of reaction

• 2 (a) For Experiment I
• Concentration of H2O2 0.14 mol dm-3
• For experiment II, hydrogen peroxide is diluted.
• (M1V1)before dilution (M2V2)after dilution
• Concentration of H2O2 after dilution

15
The effect of concentration of hydrogen peroxide
on the rate of reaction

• 2 (b) At any particular instant, the gradient of
  graph I is greater than the gradient of graph II.
  This means that the rate of reaction in
  Experiment I is faster than the rate of reaction
  in experiment II. We can therefore conclude that
  the higher the concentration of hydrogen
  peroxide, the faster the rate of reaction.

16
Factors that affect the rate of reaction

• 2 (c) The maximum volume of oxygen gas produced
  in Experiment I is twice that produced in
  Experiment II. This is because the number of
  moles of hydrogen peroxide used in Experiment I
  is twice that used in Experiment II.

17
Explaining the effectiveness of different
catalysts on the rate of decomposition of
hydrogen peroxide

• 1 Figure 1.22 shows the results of an experiment
  carried out to study the effect of different
  catalysts (of the same mass) on the rate of
  decomposition of hydrogen peroxide.

18
Explaining the effectiveness of different
catalysts on the rate of decomposition of
hydrogen peroxide

• In Experiment I, 50 cm3 of hydrogen peroxide and
  0.5 g of manganese(IV) oxide are used.
• In Experiment II, 50 cm3 of hydrogen peroxide and
  0.5 g of iron (III) oxide are used.
• For both the experiments, the concentration and
  volume of hydrogen peroxide as well as the
  temperature are kept constant.

19
Explaining the effectiveness of different
catalysts on the rate of decomposition of
hydrogen peroxide

• 2 Analysis of the reaction rate curve in Figure
  1.22
• (a) At any particular instant, the gradient of
  graph I is greater than the gradient of graph II.
  This means that the rate of reaction in
  Experiment I is faster than the rate of reaction
  in Experiment II. Thus, the experiment proves
  that manganese(IV) oxide is a more effective
  catalyst than iron(III) oxide in the
  decomposition of hydrogen peroxide.

20
Explaining the effectiveness of different
catalysts on the rate of decomposition of
hydrogen peroxide

• 2 Analysis of the reaction rate curve in Figure
  1.22
• (b) The maximum volumes of oxygen gas collected
  in both the experiments are the same because the
  volume and concentration of hydrogen peroxide
  used are the same. This experiment shows that a
  catalyst does not change the yield of the
  products.

21
Amount of catalysts on the rate of decomposition
of hydrogen peroxide

• Experiment 1.5 To Invstigate the effect of the
  amount of the catalyst, manganese (IV) oxide on
  the decomposition of hydrogen peroxide

22
Amount of catalysts on the rate of decomposition
of hydrogen peroxide

• Problem statement
• How does the amount of manganese(IV)oxide affect
  on the decomposition of hydrogen peroxide?

23
Amount of catalysts on the rate of decomposition
of hydrogen peroxide

• Hypothesis
• The rate of the decomposition of hydrogen
  peroxide increases when the amount of the
  catalyst used is increased

24
Amount of catalysts on the rate of decomposition
of hydrogen peroxide

• Variables
• (a) Manipulated variable Amount of the catalyst
  used
• (b) Responding variable The volume of oxygen
  given off at half-minute intervals
• (c) Fixed (controlled) variables Volume and
  concentration of hydrogen peroxide, temperature
  of the experiment and type of the catalyst

25
Amount of catalysts on the rate of decomposition
of hydrogen peroxide

• Apparatus
• Measuring cylinder, conical flask, delivery tube,
  rubber stopper, retort stand clamp and burette.
• Materials
• 0.2 mol dm-3 hydrogen peroxide and manganese(IV)
  oxide.

26
Amount of catalysts on the rate of decomposition
of hydrogen peroxide

• Experiment 1.5 To Invstigate the effect of the
  amount of the catalyst, manganese (IV) oxide on
  the decomposition of hydrogen peroxide

27
Amount of catalysts on the rate of decomposition
of hydrogen peroxide

• Procedure
• 1 Using a measuring cylinder, 25 cm3 of 0.2 mol
  dm-3 hydrogen peroxide is measured into a conical
  flask and 0.5 g of manganese(IV) oxide is added
  to the hydrogen peroxide.

28
Amount of catalysts on the rate of decomposition
of hydrogen peroxide

• Procedure
• 2 The conical flask is immediately closed with a
  stopper fitted with a delivery tube (Figure 1.28)
  and the stopwatch is started simultaneously. The
  conical flask is swirled gently.

29
Amount of catalysts on the rate of decomposition
of hydrogen peroxide

• Procedure
• 3 The total volume of oxygen gas given off is
  determined from the burette reading at intervals
  of ½ minute for 4 minutes.

30
Amount of catalysts on the rate of decomposition
of hydrogen peroxide

• Procedure
• 4 The experiment is repeated using 0.20 g of
  manganese(IV) oxide instead of 0.50 g of
  manganese(IV) oxide.

31
Amount of catalysts on the rate of decomposition
of hydrogen peroxide

• Results
• Experiment l.
• Decomposition of hydrogen peroxide in the
  presence of 0.5 g of manganese(IV) oxide

32
Amount of catalysts on the rate of decomposition
of hydrogen peroxide

• Results
• Experiment l.
• Decomposition of hydrogen peroxide in the
  presence of 0.2 g of manganese(IV) oxide

33
Amount of catalysts on the rate of decomposition
of hydrogen peroxide

• Discussion
• 1 Based on the results of Experiments I and II,
  two graphs of total volume of oxygen gas against
  time for the decomposition of hydrogen peroxide
  are plotted on the same axes (Figure 1.29).

34
Amount of catalysts on the rate of decomposition
of hydrogen peroxide

• Discussion
• 1 Graph I refers to the decomposition of
  hydrogen peroxide catalysed by 0.5 g of
  manganese(IV) oxide, while graph II refers to the
  decomposition of hydrogen peroxide catalysed by
  0.2 g of manganese(IV) oxide.

35
Amount of catalysts on the rate of decomposition
of hydrogen peroxide

• Discussion
• 2 The gradient of graph I is steeper than the
  gradient of graph II, This shows that the rate of
  reaction I is faster than the rate of reaction II.

36
Amount of catalysts on the rate of decomposition
of hydrogen peroxide

• Discussion
• 3 If the decomposition of hydrogen peroxide in
  both the experiments is allowed to complete, the
  maximum volumes of oxygen gas collected for both
  the experiments will be the same.

37
Amount of catalysts on the rate of decomposition
of hydrogen peroxide

• Discussion

38
Amount of catalysts on the rate of decomposition
of hydrogen peroxide

• Discussion
• 4 The quantity of catalyst does not affect the
  amount of products formed.

39
Amount of catalysts on the rate of decomposition
of hydrogen peroxide

• Conclusion
• The larger the amount of the catalyst
  manganese(IV) oxide used, the higher the rate of
  decomposition of hydrogen peroxide.

40
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• Combustion of charcoal
• 1 Large pieces of charcoal will not catch fire
  easily because the total surface area exposed to
  oxygen is small.

41
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• Combustion of charcoal
• 2 If small pieces of charcoal are used, they can
  burn easily. This is because the total surface
  area exposed to the air increases. Thus, the rate
  of reaction with oxygen (combustion) increases.

42
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• Storing food in refrigerators
• 1 The decomposition and decay of food is a
  chemical reaction caused by the action of
  microorganisms such as bacteria and fungi. These
  microorganisms multiply very rapidly at the
  temperature range of 10-60 C.

43
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• Storing food in refrigerators
• 2 Room temperature is the optimum temperature
  for the breeding of microorganisms in food. As a
  result, food turns bad quickly at room
  temperature.

44
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• Storing food in refrigerators
• 3 At low temperatures, for example, 5 C (the
  normal temperature of a refrigerator), the
  activities of bacteria are slowed down. Hence,
  food that is kept in a refrigerator will last
  longer because the decaying reaction that
  destroys the food can be slowed down.

45
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• Storing food in refrigerators
• 4 In the supermarkets, fish, meat and other
  types of fresh foods are kept in deep-freeze
  compartments where the temperature is about -20
  C. This keeps the food fresh for a few months
  because the very low temperature slows down the
  chemical reactions that cause the food to decay.

46
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• Cooking food in pressure cookers
• 1 Pressure cookers are used to speed up cooking.

47
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• Cooking food in pressure cookers
• 2 In the pressure cooker, the higher pressure
  enables water or oil to boil at a temperature
  higher than their normal boiling points.
  Furthermore, an increase in pressure causes an
  increase in the number of water molecules or
  cooking oil molecules coming into contact and
  colliding with the food particles.

48
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• Cooking food in pressure cookers
• 3 At a higher temperature and pressure, the rate
  of reaction becomes faster. Thus, food cook
  faster in pressure cookers.

49
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• Uses of catalysts in industry
• 1 From the economic point of view, catalysts
  play a vital role in industrial processes.

50
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• Uses of catalysts in industry
• 2 Catalysts do not increase the yields of
  reactions. However, catalysts are used widely in
  industrial processes to speed up the rates of
  reactions so that the same amount of products can
  be obtained in a shorter time. As a result, the
  use of catalysts brings down the cost of
  production.

51
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• Uses of catalysts in industry
• 3 In the chemical industry, small pellets of
  solid catalysts are used instead of big lumps.
  This is to give a larger surface for catalytic
  reaction to occur and hence a faster reaction
  will result.

52
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• The manufacture of ammonia (Haber process)
• 1 The Haber process is an industrial process for
  the manufacture of ammonia from nitrogen and
  hydrogen.

53
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• The manufacture of ammonia (Haber process)
• 2 Nitrogen and hydrogen do not react at room
  temperature and pressure. High temperature and
  pressure and the presence of a catalyst are
  required for nitrogen to react with hydrogen.

54
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• The manufacture of ammonia (Haber process)
• 3 The optimum conditions for obtaining a maximum
  yield of ammonia in the Haber process are as
  follows
• (a) Temperature 450-550 oC
• (b) Pressure 200-500 atmospheres
• (c) Catalyst Finely divided iron (Fe)

55
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• The manufacture of ammonia (Haber process)
• 4 In terms of industrial processes, a
  temperature of 450 C is considered as moderately
  high but the rate of reaction is slow at this
  temperature. Thus, a catalyst is required to
  increase the rate of reaction.

56
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• 5 In the Haber process, ammonia is produced when
  a mixture of nitrogen and hydrogen (in the ratio
  of 13 by volume) is passed over finely divided
  iron as catalyst at 450-500 C and 200-500
  atmospheres. Under these conditions, about 10
  yield of ammonia is obtained.

57
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• The manufacture of sulphuric add (Contact
  process)
• 1 The contact process is the industrial process
  for the manufacture of sulphuric acid from
  sulphur and oxygen.

58
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• The manufacture of sulphuric add (Contact
  process)
• Raw materials required sulphur, air and water.
• Conditions for the reaction of SO2 with O2 (from
  the air)
• (a) Temperature 450-500 C
• (b) Pressure 1-2 atmospheres
• (c) Catalyst Vanadium(V) oxide, V2O5

59
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• 2 The following reaction scheme shows the steps
  involved in the manufacture of sulphuric acid

60
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• 3 In Step 2, sulphur dioxide is oxidised to
  sulphur trioxide. The mixture of sulphur dioxide
  and oxygen is passed over vanadium(V) oxide,
  V2O5, as catalyst at 450-500 C and a pressure of
  1-2 atmospheres to form sulphur trioxide. Under
  these conditions, a yield of 98 of sulphur
  trioxide is obtained.

61
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• The manufacture of nitric acid (Ostwald process)
• 1. The Ostwald process is used to manufacture
  nitric acid.
• Raw materials required ammonia, air and water
• Conditions
• (a) Temperature 900 C
• (b) Pressure 1-8 atmospheres
• (c) Catalyst platinum

62
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• The manufacture of nitric acid (Ostwald process)
• The following reaction scheme shows the steps
  involved in the manufacture of nitric acid.

63
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• The manufacture of nitric acid (Ostwald process)
• 2 In the Ostwald process, nitrogen monoxide, NO,
  is produced (step 1) when ammonia gas is passed
  over the platinum (Pt) catalyst at about 900 C
  and 1-8 atmospheres.
• In this reaction, ammonia is oxidised to nitrogen
  monoxide.

64
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• Example 5
• Two experiments were carried out to determine the
  rate of producing oxygen gas during the
  decomposition of hydrogen peroxide. In Experiment
  I, 20 cm3 of 2 moldm-3 hydrogen peroxide were
  used and the results of the experiment are shown
  on graph I in Figure 1.26.

65
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• Example 5
• (a) Sketch a graph on the same axes to show the
  results of the experiments that will be obtained
  if 5 cm3 of 4 mol dm-3 hydrogen peroxide were
  used for the reaction.

66
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• Example 5
• Solution
• (a)

67
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• Example 5
• (b) Explain your answer in (a).

68
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• Example 5
• Solution
• (b) Differences in terms of rate of reaction
• Graph II is steeper than graph I because the rate
  of reaction in Experiment II is expected to be
  faster than Experiment I. When the concentration
  of hydrogen peroxide is increased from 2 moldm-3
  to 4 mol dm-3, the rate of reaction also
  increases

69
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• Example 5
• Solution
• (b) Number of moles of H2O2 used in Experiment I

70
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• Experiment 6
• Solution
• (b) Number of moles of H2O2 used in Experiment I
• ?Volume of oxygen collected at room temperature
  in Experiment I

2H2O2 (aq) ? 2H2O(l) O2 (g)
2mol
1mol
71
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• Experiment 6
• Solution
• (b) Number of moles of H2O2 used in
• Experiment II

72
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• Example 5
• Solution
• (b) Volume of oxygen collected at room
  temperature in Experiment II

73
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• Example 5
• (c) State the controlled variables for both the
  experiments.

74
Applications of factors that affect rates of
reaction in daily life and in industrial processes

• Example 5
• Solution
• (c) Fixed (controlled) variables
• In both the experiments, the same mass of the
  catalyst and the same temperature of reaction are
  used.