Activated complex (chemistry)

Potential energy diagram for a hypothetical reaction A + B → C + D, where E_a is the energy of activation and ΔH the increase of the reaction detail.

In chemistry, an activated complex of an elementary chemical reaction is the particular arrangement of atoms at the top of the energy barrier. If we represent its energy against all the coordinates of the system, we will generally see how it is an energetic minimum in all of them, except in the reaction coordinate -which leads from reactants of the reaction to its products-, in which it is a maximum.

The stabilization of the activated complex, for example, through enzymes (or catalysts in general) generally leads to a substantial acceleration of the reaction.