Activation energy is the minimum energy needed for ‘successful collisions’ where atoms within the reactants rearrange to form products. It can be represented on an energy level diagram.

Enzymes lower the activation energy necessary to transform a reactant into a product. On the left is a reaction that is not catalyzed by an enzyme (red), and on the right is one that is (green).

A reaction profile includes the activation energy, which is the minimum energy needed by particles when they collide for a reaction to occur. The activation energy is shown as a 'hump' in the line ...

On the right, the direct burning of sugar requires a larger activation energy. In this reaction, the same total free energy is released as in stepwise oxidation, but none is stored in carrier ...