Catalysts work by providing an alternative reaction route with a lower activation energy.
Intermediate Formation Theory of Catalysis
The reactant molecules and the catalyst form and unstable intermediate complex that breaks up to form products and regenerate the catalyst
How does the reaction of aqueous cobalt (II) chloride between H2O2 and potassium sodium tartrate give evidence for the intermediate formation theory of catalysis?
- Initial solution is pink
- During reaction, there is a colour change from pink to green [intermediate complex formed]
- Frothing and bubbling reaction [fast rate of reaction - products formed]
- Reaction returns to pink [catalyst regenerated]
Surface Adsorption Theory of Catalysis
The reactant molecules adsorb onto solid catalyst where the greater local concentration leads to a quick reaction – bonds formed must be strong enough to adsorb and increase concentration, but weak enough to decompose quickly and form products
How does the oxidation of methanol using a hot platinum catalyst provide evidence for the surface adsorption theory of catalysis?
- Series of mild explosions and glowing platinum [fast exothermic rate of reaction]
- H atoms are removed more quickly by reactant adsorbing to surface of catalyst which weakens and breaks bonds.
Catalytic Poisons
When the active sites of the catalyst are blocked by substances bonding to it more strongly than the reactants, the catalyst is poisoned
e.g. Lead, arsenic, sulfur
