Catalysts

• What is a catalyst?

  A catalyst is a substance that changes the rate of a chemical reaction without undergoing any permanent change itself

  1. the catalyst is not used up in the chemical reaction
  2. the catalyst may react with a reactant to form an intermediate or may provide a surface on which the reaction can take place
  3. at the end of the reaction the catalyst is regenerated
• How does a catalyst increase the rate of a chemical reaction?

  By providing an alternative reaction pathway of lower activation energy
• What is a homogeneous catalyst?

  A catalyst that has the same physical state as the reactants. The catalyst reacts with the reactants to form an intermediate. The intermediate then breaks down to give the product and regenerates the catalyst.
• Give an example of a reaction that uses a homogeneous catalyst?

  (usually gases or liquids)

  1. making esters with sulfuric acid as a catalyst for example making the ester CH5COOC2H5 from ethanoic acid, CH3COOH and ethanol, C2H5OH with sulfuric acid as the catalyst, H2SO4
  2. ozone depletion (Cl radicals as catalyst) depletion of ozone, O3 in the presence of chlorine radicals which act as a catalyst 2O3 (g) = 3O2
• What are heterogeneous catalysts?

  catalysts that have a different physical state from the reactants. Usually solids in contact with gaseous reactants or reactants in solution.
• How do heterogeneous catalysts work?

  Reactant molecules are adsorbed (weakly bonded) onto the surface of the catalyst, where the reaction takes place. After reaction, the product molecules leave the surface of the catalyst by desorption