Catalysts (Oxford AQA International A Level (IAL) Chemistry): Revision Note

Catalysts & Rate of Reaction

• Catalysis is the process in which the rate of a chemical reaction is increased, by adding a catalyst

• A catalyst increases the rate of a reaction by providing the reactants with an alternative reaction pathway which is lower in activation energy than the uncatalysed reaction

• Catalysts can be divided into two types:

  • Homogeneous

  • Heterogeneous

• Homogeneous means that the catalyst is in the same phase as the reactants, for example

  • Concentrated sulfuric acid in esterification

• Heterogeneous means that the catalyst is in a different phase to the reactants, for example

  • Aluminium oxide in cracking hydrocarbon chains from crude oil

  • Iron in the Haber process (production of ammonia)

  • Catalytic convertors in cars exhausts

Maxwell-Boltzmann distribution curve

• Catalysts provide the reactants another pathway which has a lower activation energy

• By lowering E_a, a greater proportion of molecules in the reaction mixture have the activation energy, and therefore 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