Catalyst vs. Intermediate Species

[Rhiannon Imbeah 2I]

What is the difference between a catalyst and an intermediate species?

[cara_Budzinski_3D]

An intermediate species is cancelled out in a multi-step reaction. For example, in a 2 step reaction if the product of Step One is a reactant in Step Two, then it is an intermediate. This is because does not appear in the initial reactants or final products. Catalysts, in contrast, provide a new pathway with lower activation energy for the reaction and are NOT consumed in the reaction.

[vannahyazon 1L]

If we're describing catalysts and intermediates in free energy diagrams,

The catalyst is not specifically drawn in the diagram, but it will decrease the activation energy. So you will draw your deltaG curve smaller than before the catalyst was put in.

Intermediates are represented by the valley in between two transition states curves (TS1 & TS2).