Catalysts

• Catalyst is a substance that affects the rate of chemical reactions without being chemically changed themselves at the end of the reaction
• Catalysts work by providing a different pathway for the reaction with a lower activation energy
• Catalysts do not affect the enthalpy change of a reaction, nor do they affect the position of equilibrium in a reversible reaction.
• Iron is the catalyst used in the Haber process
• Zeolite is the catalyst used in cracking
• Reactions on a catalyst take place in two steps:

  • Adsorption
  • Desorption
• Adsorption


  The gases first form weak bonds with the metal atoms of the catalyst, this holds them in the correct position for them to react together.
• Desorption


  The products break away from the metal atoms, which frees up room on the catalysts surface for more gasses to react
• The strength of the weak bonds holding the gases onto the metal surface is very important.

  • Must be strong enough to hold the gases for long enough to react
  • Must be weak enough to release the products easily