Download - 1.4 Rate of Reaction(1.2d)
Effect of Catalyst on the rate of Effect of Catalyst on the rate of reactionreaction
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 Effect of Catalyst on the rate of reactionreaction
Problem statement How do catalyst affect the rate of decomposition of
hydrogen peroxide
Effect of Catalyst on the rate of Effect of Catalyst on the rate of reactionreaction
Hypothesis Manganese (IV) oxide speed up the
decomposition of hydrogen peroxide
Effect of Catalyst on the rate of Effect of Catalyst on the rate of reactionreaction
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 Effect of Catalyst on the rate of reactionreaction
Apparatus Boiling tube and wooden splinter
Material Hydrogen peroxide and manganese (IV) oxide
Effect of Catalyst on the rate of Effect of Catalyst on the rate of reactionreaction
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 Effect of Catalyst on the rate of reactionreaction
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 Effect of Catalyst on the rate of reactionreaction
Results
Effect of Catalyst on the rate of Effect of Catalyst on the rate of reactionreaction
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 Effect of Catalyst on the rate of reactionreaction
Discussion 2 The glowing splinter is rekindled in the
presence of oxygen gas.
Effect of Catalyst on the rate of Effect of Catalyst on the rate of reactionreaction
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 The effect of concentration of hydrogen peroxide on the rate of reactionperoxide 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 The effect of concentration of hydrogen peroxide on the rate of reactionperoxide 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 The effect of concentration of hydrogen peroxide on the rate of reactionperoxide 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
307.050
2514.0
moldm
The effect of concentration of hydrogen The effect of concentration of hydrogen peroxide on the rate of reactionperoxide 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 Factors that affect the rate of reactionreaction
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 Explaining the effectiveness of different catalysts on the rate of decomposition of catalysts on the rate of decomposition of
hydrogen peroxidehydrogen 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 Explaining the effectiveness of different catalysts on the rate of decomposition of hydrogen peroxidethe 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 Explaining the effectiveness of different catalysts on the rate of decomposition of hydrogen peroxidethe 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 Explaining the effectiveness of different catalysts on the rate of decomposition of hydrogen peroxidethe 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 Amount of catalysts on the rate of decomposition of hydrogen peroxidehydrogen 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 Amount of catalysts on the rate of decomposition of hydrogen peroxidehydrogen 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 Amount of catalysts on the rate of decomposition of hydrogen peroxidehydrogen 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 Amount of catalysts on the rate of decomposition of hydrogen peroxidehydrogen 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 Amount of catalysts on the rate of decomposition of hydrogen peroxidedecomposition 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 Amount of catalysts on the rate of decomposition of hydrogen peroxidedecomposition 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 Amount of catalysts on the rate of decomposition of hydrogen peroxidedecomposition 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 Amount of catalysts on the rate of decomposition of hydrogen peroxidedecomposition 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 Amount of catalysts on the rate of decomposition of hydrogen peroxidedecomposition 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 Amount of catalysts on the rate of decomposition of hydrogen peroxidedecomposition 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 Amount of catalysts on the rate of decomposition of hydrogen peroxidedecomposition 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 Amount of catalysts on the rate of decomposition of hydrogen peroxidedecomposition 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 Amount of catalysts on the rate of decomposition of hydrogen peroxidedecomposition 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 Amount of catalysts on the rate of decomposition of hydrogen peroxidedecomposition 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 Amount of catalysts on the rate of decomposition of hydrogen peroxidedecomposition 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 Amount of catalysts on the rate of decomposition of hydrogen peroxidedecomposition 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 Amount of catalysts on the rate of decomposition of hydrogen peroxidedecomposition of hydrogen peroxide
Discussion
Amount of catalysts on the rate of Amount of catalysts on the rate of decomposition of hydrogen peroxidedecomposition of hydrogen peroxide
Discussion 4 The quantity of catalyst does not affect
the amount of products formed.
Amount of catalysts on the rate of Amount of catalysts on the rate of decomposition of hydrogen peroxidedecomposition 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 Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses 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 Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses 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 Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses 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 Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses 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 Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses 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 Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses 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 Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses Cooking food in pressure cookers 1 Pressure cookers are used to speed up
cooking.
Applications of factors that affect rates Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses 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 Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses 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 Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses 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 Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses 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 Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses 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 Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses 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 Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses 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 Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses 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 Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses 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 Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses 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 Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses 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 Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses 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 Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses 2 The following reaction scheme shows the steps
involved in the manufacture of sulphuric acid:
Applications of factors that affect rates Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses 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 Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses 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 Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses 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 Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses 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 Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses 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 Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses 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 Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses Example 5 Solution (a)
Applications of factors that affect rates Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses Example 5 (b) Explain your answer in (a).
Applications of factors that affect rates Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses 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 Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses Example 5 Solution (b) Number of moles of H2O2 used in Experiment I
mol04.01000
202
Applications of factors that affect rates Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses Experiment 6 Solution (b) Number of moles of H2O2 used in Experiment I
Volume of oxygen collected at room temperature in Experiment I
mol04.01000
202
34802400004.02
1cm
2H2O2 (aq) 2H2O(l) + O2 (g)
2mol 1mol
Applications of factors that affect rates Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses Experiment 6 Solution (b) Number of moles of H2O2 used in
Experiment II= mol02.01000
54
Applications of factors that affect rates Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses Example 5 Solution (b) Volume of oxygen collected at room
temperature in Experiment II
=3240480
2
1cm
Applications of factors that affect rates Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses Example 5 (c) State the controlled variables for both the
experiments.
Applications of factors that affect rates Applications of factors that affect rates of reaction in daily life and in industrial of reaction in daily life and in industrial
processesprocesses 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.