Effect of Catalyst on the rate of reaction

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					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
Effect of Catalyst on the rate of
            reaction
   Problem statement
   How do catalyst affect the rate of decomposition
    of hydrogen peroxide
Effect of Catalyst on the rate of
            reaction
   Hypothesis
   Manganese (IV) oxide speed up the
    decomposition of hydrogen peroxide
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
Effect of Catalyst on the rate of
            reaction
   Apparatus
   Boiling tube and wooden splinter

   Material
   Hydrogen peroxide and manganese (IV) oxide
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).
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.
Effect of Catalyst on the rate of
            reaction
   Results
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)
Effect of Catalyst on the rate of
            reaction
   Discussion
   2 The glowing splinter is   rekindled in the
    presence of oxygen gas.
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.
     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.
     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.
        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

               0.14  25
                         0.07moldm3
                  50
     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.
    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.
     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.
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.
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.
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.
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
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?
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
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
     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.
     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
     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.
     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.
     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.
     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.
     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
     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
     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).
     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.
     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.
     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.
     Amount of catalysts on the rate of
    decomposition of hydrogen peroxide
   Discussion
     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.
     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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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)
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.
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 1:3 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.
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.
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
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:
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.
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
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.
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.
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.
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.
Applications of factors that affect rates
of reaction in daily life and in industrial
                processes
   Example 5
   Solution
   (a)
Applications of factors that affect rates
of reaction in daily life and in industrial
                processes
   Example 5
   (b) Explain your answer in (a).
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
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
          2  20
                 0.04mol
          1000
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
          2  20
                 0.04mol 2H2O2 (aq)  2H2O(l) + O2 (g)
          1000              2mol                 1mol
   Volume of oxygen collected at room temperature
    in Experiment I
        1
         0.04  24000  480cm3
        2
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
                   45
   Experiment II=       0.02mol
                   1000
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
       1
   = 2   480  240cm3
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.
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.

				
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posted:12/15/2011
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