Types of Catalyst (Cambridge (CIE) AS Chemistry): Revision Note

Explaining How Catalysts Work

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

  • Heterogeneous catalysts

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

  • For example, the reactants and the catalyst are all liquids

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

  • For example, the reactants are gases, but the catalyst used is a solid

How a catalyst works 

How catalysts affect the reaction pathway

Boltzmann distribution curve

• Catalysts enable the reaction to proceed via an alternative pathway with lower activation energy

• By lowering E_a, 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 uncatalysed reaction

How catalysts affect the number of particles with sufficient energy to react (E_a)