Activation Energy (Eat)
It is the minimum energy that reagents need to initiate the chemical reaction. This minimum energy is required for the formation of the activated complex.
The higher the activation energy, the slower the reaction, because it increases the difficulty for the process to occur. The lower the activation energy, the lower the energy "barrier", the more effective collisions and therefore a faster reaction.
Endothermic and exothermic graphs for activation energy
The activation energy varies according to the type of chemical reaction. In endothermic reactions it is larger than in exothermic ones.