CIE AS Chemistry (9701) exams from 2022

Revision Notes

1.8.4 Homogeneous & Heterogeneous Catalysts

Catalysts

Reaction pathway diagram

  • Catalysis is the process in which the rate of a chemical adding substances that themselves do not take part in the reaction
  • A catalyst is a substance that increases the rate of a reaction by providing the reactants with a different reaction pathway which is lower in activation energy than the uncatalyzed reaction

 

Reaction Kinetics Catalyst, downloadable AS & A Level Chemistry revision notes

The diagram shows that the catalyst speeds up a reaction that would normally be slow due to the high activation energy. The catalyst is not used up in the chemical reaction and is not taking part in the chemical reaction

Reaction Kinetics Catalyst Reaction Pathway, downloadable AS & A Level Chemistry revision notes

The diagram shows that the catalyst allows the reaction to take place through a different mechanism, which has a lower activation energy than the original reaction

Boltzmann distribution curve

  • Catalyst provide the reactants another pathway which has a lower activation energy
  • By lowering Ea, a greater proportion of molecules in the reaction mixture have sufficient energy for an effective collision
  • As a result of this, the rate of the catalysed reaction is increased compared to the uncatalyzed reaction

 

Reaction Kinetics Catalyst Boltzmann Distribution, downloadable AS & A Level Chemistry revision notes

The diagram shows that the total shaded area (both dark and light shading) under the curve shows the number of particles with energy greater than the Ea when a catalyst is present. This area is much larger than the dark shaded area which shows the number of particles with energy greater than the Ea without a catalyst

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Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.
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