Catalysts

Things that Effect Rate l Catalysts- substances that speed up a reaction without being used up.(enzyme). l Speeds up reaction by giving the reaction a new path. l The new path has a lower activation energy. l More molecules have this energy. l The reaction goes faster. l Inhibitor- a substance that blocks a catalyst.

Energy Reaction coordinate Reactants Products

Homogenous Catalyst l Catalyst present in the same phase as the components of the reaction l Example: NO acts as a catalyst for the decomposition of ozone l NO provides another mechanism for the reaction which has a lower E a

Heterogeneous Catalyst l Exists in a phase different from reactants l Catalyzed reactions of gases often occur at the surface of metals l Places where reacting molecules are absorbed on the metal surface are called active sites

Pt surface HHHH HHHH l Hydrogen bonds to surface of metal. l Break H-H bonds Catalysts

Pt surface HHHH Catalysts C HH C HH

Pt surface HHHH Catalysts C HH C HH l The double bond breaks and bonds to the catalyst.

Pt surface HHHH Catalysts C HH C HH l The hydrogen atoms bond with the carbon

Pt surface H Catalysts C HH C HH HHH

Example A reaction occurs in a two step mechanism as shown A + C → B + D (slow) B + A → C + F (fast) a) What substance acts as a catalyst? b) What substance is an intermediate? c) Write the overall reaction equation. d) Write the rate law for the overall reaction.