The Principles of Catalysis

Enthalpy profile for a catalysed reaction

A catalyst interacts with reactant molecules to provide an alternative pathway for the reaction involving a lower activation than that of the non–catalysed reaction. More of the reactant molecules have energies that are bigger than this lower activation enthalpy. Therefore more of the collisions result in a successful reaction and the rate of conversion of reactant to product is increased.

What's the alternative pathway?

The catalyst interacts with the reactants to form an intermediate complex. This is sometimes called a transition state. The complex breaks down to give products and the catalyst. The catalyst is freed to interact with further reactants and so the reaction continues.

A catalyst provides an alternative pathway - reducing the activation energy