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Starter: 1)Definition of catalysts: 2) Difference between homogeneous and heterogeneous catalyst.

Starter: 1)Definition of catalysts: 2) Difference between homogeneous and heterogeneous catalyst. 3) Do catalyst last for ever? 4) Give examples of catalysts. Catalysis. L.O.: What heterogeneous and homogeneous catalysts are. How heterogeneous catalyst be made more efficient.

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Starter: 1)Definition of catalysts: 2) Difference between homogeneous and heterogeneous catalyst.

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  1. Starter: 1)Definition of catalysts: 2) Difference between homogeneous and heterogeneous catalyst. 3) Do catalyst last for ever? 4) Give examples of catalysts.

  2. Catalysis L.O.: What heterogeneous and homogeneous catalysts are. How heterogeneous catalyst be made more efficient. How a homogeneous catalyst works.

  3. INTRODUCTION • Catalyst = substance that speeds up reaction without being used up. • They provide an alternative mechanism with lower activation energy. • For an equilibrium, they speed up both reactions equally and so do not effect equilibrium position. • Heterogeneous catalyst is in different phase to the reactants. • Homogeneous catalyst is in the same phase as the reactants.

  4. INTRODUCTION

  5. HETEROGENEOUS CATALYSTS • Usually a solid catalyst and gaseous reactants. • Most industrial catalysts are like this (e.g. Haber, Contact).

  6. HETEROGENEOUS CATALYSTS

  7. HETEROGENEOUS CATALYSTS 1) Reactants adsorbed onto surface (onto active sites). • weakens bonds • brings molecules closer • more favourable orientation 2) Reaction takes place. 3) Products are desorbed (leave the surface). Animation

  8. Discuss in groups: how could a heterogeneous catalysts be made more efficient?

  9. HETEROGENEOUS CATALYSTS Nature of catalyst • Large surface area. • Spread thinly over ceramic honeycomb.

  10. HETEROGENEOUS CATALYSTS Poisoning • Some substances may block active sites (i.e. they adsorb and will not come off). Can ruin catalyst. • e.g. S in Haber process • e.g. Pb in catalytic converters

  11. HOMOGENEOUS CATALYSTS e.g. acid catalyst in esterification e.g. CH3COOH(l) + CH3OH(l)  CH3COOCH3(l) + H2O(l) No H+ catalyst SLOW step With H+ catalyst FASTER

  12. HOMOGENEOUS CATALYSTS e.g. transition metal catalyst works by metal varying oxidation state Fe2+or Fe3+ e.g. 2 I- + S2O82-→ I2 + 2 SO42- Slow because both –ve ions so repel. • 2 Fe2+ + S2O82-→ 2 Fe3+ + 2 SO42- • 2) 2 Fe3+ + 2 I-→ 2 Fe2+ + I2

  13. HOMOGENEOUS CATALYSTS + 0 + 0.54 V + 1.51 V I2 + 2 e- 2 I- S2O82- + 2 e- 2 SO42- + 0.77 V Fe3+ + e- Fe2+

  14. HOMOGENEOUS CATALYSTS e.g. transition metal catalyst works by metal varying oxidation state Mn2+ e.g. 2 MnO4- + 16 H+ + 5 C2O42-→ 2 Mn2+ + 8 H2O + 10 CO2 the reaction is catalysed by one of the products (Mn2+) – this is called autocatalysis

  15. Worksheet 14.4

  16. Catalysis L.O.: What heterogeneous and homogeneous catalysts are. How heterogeneous catalyst be made more efficient. How a homogeneous catalyst work.

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