1 / 16

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.

sydney
Télécharger la présentation

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

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  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.

More Related