Catalysts

• Why are transition metals good catalysts?

  Can change oxidation states by gaining or losing electrons within their d orbitals. Can transfer electrons to speed up reactions.
• What are heterogenous catalysts?

  In a different phase from the reactants.
• What happens when a heterogenous catalyst is used?

  Reaction happens on surface of catalyst. Increasing surface area of catalyst increases number of molecules that can react at the same time- increases reaction rate. Support medium can make catalyst area larger.
• How can catalyst poisoning occur?

  In reaction, reactants adsorbed onto active sites on surfaces of heterogenous catalysts. Impurities in reaction mixture may also bind to catalyst surface & block reactants being adsorbed (catalyst poisoning). Reduces surface area of catalysts available to reactants, slowing reaction. Increases cost as less product made in certain time or with certain amount of energy. Catalyst may need replacing/regenerating- costs money. Reduced catalyst poisoning by purifying reactants.
• What happens in the contact process?

  V2O5 oxidises SO2 into SO3, & is reduced to V2O4. V2O4 oxidised by O2 back into V205.
• What are homogenous catalysts?

  Same physical state as reactants.
• How does a homogenous catalyst work?

  Forming intermediate species. Reactants combine with catalyst to make intermediate species, which reacts to form products & reform catalyst.
• Why is the redox reaction initially slow?

  Both negative ions so repel eachother- unlikely to collide & react. Higher activation energy.
• Reaction catalysed by Fe 2+


  S2O8 2- + 2I- -> I2 + 2S04 2-
• How does Mn 2+ autocatalyse MnO4- & C2O4 2- reaction?

  Mn2+ product & catalyst. As reaction progresses & product increases, reaction speeds up.