30 Questions
What is the rate of reaction proportional to in the oxidation of thiosulphate by H2O2 in presence of iodide ions as catalyst?
Concentrations of Peroxide and iodide only
What is the main difference between heterogeneous catalysis and other types of catalysis?
The catalyst and the reaction mixture are in different phases
What is the product of the hydrogenation of carbon-carbon double bond reaction?
CH3CH3
What is synthesized by contacting carbon monoxide, carbon dioxide, and hydrogen with copper/zinc oxide catalyst?
Methanol
What is the primary function of catalytic converters?
To reduce the emissions of pollutants
What type of catalysts are used in catalytic converters?
Expensive metals like platinum, palladium, and rhodium
What is the primary mechanism of heterogeneous catalysis?
All of the above
What is the result of the reaction between ethene and hydrogen in presence of nickel as a catalyst?
CH3CH3
What is the activation energy for the uncatalysed decomposition of hydrogen peroxide?
75 kJmol-1
Which catalyst is used in the Haber’s process for the synthesis of ammonia?
Tungsten
What is the product of the decomposition of hydrogen iodide?
H2(g) + I2(g)
What is the activation energy for the catalysed decomposition of hydrogen peroxide using the enzyme?
23 kJmol-1
What is the equation for the decomposition of hydrogen peroxide?
2 H2O2(aq) ===> 2 H2O(l) + O2(g)
What is the role of the catalyst in the Haber’s process?
To decrease the activation energy
What is the overall reaction in the oxidation of carbon monoxide using transition metal oxides?
2CO + O2 → 2CO2
What type of oxides are used in dehydration reactions?
Acidic oxides
What is the role of vanadium(V) oxide in the contact process?
To convert sulphur dioxide into sulphur trioxide
What is the characteristic of p-type metal oxides?
Excess positive charges in the solid
What is the function of molybdenum disulfide in low sulfur fuels?
To facilitate the removal of sulphur
What is the type of catalyst used in the oxidation of carbon monoxide?
Heterogeneous catalyst
What is the role of basic oxides in catalysis?
To favor reactions involving anionic species
What is the purpose of the contact process?
To manufacture sulphuric acid
According to the theory of activated complex, what determines the overall rate of catalytic reaction?
The rate of dissociation of the active complex into the final product
What is the expression for the overall rate of reaction according to the steady state theory?
d[P]/dt = K1 K3 [A] [B] [C] / (K2 + K3 [B])
What is the relationship between the rate of catalytic process and the concentration of reactants and catalyst?
The rate is directly proportional to the concentration of both reactants and catalyst
What is the condition for the Arrhenius approach?
K2 is much larger than K3
What is the expression for [ABC] according to the steady state theory?
[ABC] = (K3 / K4) [AC] [B]
What is the experimental example of the Arrhenius type reaction?
Oxidation of thiosulphate with H2O2 using molebdenic acid as catalyst
What is the rate of reaction in the Arrhenius approach?
Rate of reaction = [A] [B] [C]
What is the intermediate complex formed in the catalytic reaction?
AC
Study Notes
Kinetic Treatment of Catalytic Homogeneous Reactions
- The overall rate of catalytic reaction is determined by the rate of dissociation of the active complex into the final product.
- The rate of activated complex formation can be represented as
d[ABC]/dt = K3[AC][B] - K4[ABC] = 0. - The rate of formation of intermediate AC can be given as
d[AC]/dt = K1[A][C] - K2[AC] - K3[AC][B] = 0. - The overall rate of reaction is represented as
d[P]/dt = (K1K3[K2 + K3[B]][A][B][C].
Approaches to Catalytic Reactions
- Arrhenius approach: rate constant K2 is much larger than K3, so the rate of reaction is proportional to
[A][B][C]. - Van't Hoff approach: rate constant K3 is much larger than K2, so the rate of reaction is proportional to
K1[A][C].
Heterogeneous Catalysis
- Heterogeneous catalysis involves a catalyst and reaction mixture in different phases.
- Examples of heterogeneous catalysis include:
- Hydrogenation of carbon-carbon double bond using nickel as a catalyst.
- Methanol synthesis using copper/zinc oxide catalyst.
- Catalytic converters using platinum, palladium, and rhodium to convert carbon monoxide and nitrogen oxides into carbon dioxide and nitrogen.
- The use of vanadium(V) oxide in the contact process for manufacturing sulfuric acid.
- Oxidation of carbon monoxide using transition metal oxides such as nickel oxide.
- Acidic oxides (dehydration process) such as Al2O3 and SiO2.
- Basic oxides (dehydrogenation process) such as MgO and ZrO.
- Low sulfur fuels: desulfurization catalysis using molybdenum disulfide.
Comparing Activation Energies
- The decomposition of hydrogen peroxide:
- Uncatalysed: 75 kJmol-1
- Catalysed with colloidal platinum: 49 kJmol-1
- Catalysed by the enzyme: 23 kJmol-1
- The decomposition of hydrogen iodide:
- Uncatalysed: 183 kJmol-1
- Au catalysed: 105 kJmol-1
- Pt catalysed: 58 kJmol-1
- The synthesis of ammonia (Haber's process):
- Uncatalysed: 350 kJmol-1
- Transition metal tungsten (W) catalyst: 162 kJmol-1
This quiz covers the kinetic treatment of catalytic homogeneous reactions, including the role of activated complex theory in determining the overall rate of reaction.
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