1. Theories of Catalysis
How catalysts work

2. Surface Adsorption Theory
Reactants adsorbed onto the surface
This increases concentration of the reactants and so speeds up the reaction
May also twist the molecules of reactants so that they find it easier to react
Many enzymes work in this way
Called Lock and Key Theory

3. Intermediate Compound Theory
Formation of ethene [C2H4] from alcohol [C2H5OH]
catalyst reduces activation energy
C2H5OH = C2H H2O
C2H5OH + H2SO = C2H5HSO4 + H2O
C2H5HSO = C2H H2SO4
180oC

4. CoCl2 used to catalyse the reaction between tartaric acid and hydrogen peroxide
the CoCl2 solution went green as it formed the intermediate compound and then returned to pink as the reaction finished.
This was the catalyst returning to it original condition

5. Autocatalysts
In some reactions one of the products of the reaction catalyses the reaction - this product is called an autocatalyst.
Mn2+ in MnO4- titrations [permanganate or manganate(VII)]
First drop slow to lose purple colour because reaction is slow but
second and subsequent drops decolourise faster because the Mn2+ catalyses the reaction

6. Catalytic Poisons
Substances that stop catalysts working are called catalytic poisons
e.g. Heavy metals such as lead
Hence don’t use leaded petrol if you have a catalytic converter

7. 6.2e Homogeneous and Heterogeneous Catalysts

8. 2 SO2(g) + O2(g) = 2 SO3(g) catalyst V2O5(s)
If the catalyst and the reactants are in different phases [states] the catalyst is said to be heterogeneous
E.g. Fe in the Haber Process for the industrial production of ammonia
The iron [solid] and the nitrogen and hydrogen [gases] are in different phases
N2(g) H2(g) = 2 NH3(g)
2 SO2(g) + O2(g) = 2 SO3(g) catalyst V2O5(s)
Part of the Contact Process for the industrial production of sulphuric acid
Fe(s)

9. Homogeneous
H2O2 = H2O + ½ O2
Potassium iodide solution catalyses the decomposition of hydrogen peroxide solution
Both the catalyst and the reactant are in the same phase (liquid / solution) i.e. there is no boundary between the reactants and catalyst
One of the products is a gas but products don’t count only reactants and catalyst
KI(aq)