Homogenous Catalysts

Catalysts that are in the same physical state as the reactants

An aqueous catalyst for a reaction between two aqueous solutions

Work by combining with the reactants to form an intermediate species which then reacts to form the products and reform the product

Has two humps in it, corresponding to the two parts/steps of the reaction

Ea needed to form the intermediates (and to form the products from the intermediates) is lower than that needed to make the products directly from the reactants

Always re-forms. So it can carry on catalysing the reaction

The redox reaction is slow because both ions are negatively charged. The ions repel each other, due to the negative charges. So the ions are unlikely to collide and react due to the reaction having a high activation energy

Fe 2+ ions are oxidised to Fe 3+ ions by the S2O8 2- ions. The newly formed intermediate Fe 3+ ions now easily oxidise the I- ions to iodine, and the catalyst is regenerated. Because each stage of the reaction involves a positive and negative ion, so there’s no repulsion

S2O8 2- + 2Fe 2+ –> 2Fe 3+ + 2SO4 2- 2Fe 3+ + 2I- –> I2 + 2Fe 2+ All are aqueous

Where a product of a reaction acts as a catalyst

As the reaction progresses and the amount of product increases, the reaction speeds up

Mn 2+ is a homogenous catalyst for the reaction between C2O4 2- and MnO4-. Mn 2+ catalyses the reaction by first reacting with MnO4- to form Mn3+ ions. The newly formed Mn3+ ions then react with C2O4 2- to form carbon dioxide and re-form the Mn2+ catalyst ions

MnO4- + 4Mn 2+ + 8H+ –> 5Mn 3+ + 4H2O 2Mn3+ + C2O4 2- –> 2Mn2+ + 2CO2