4.19      understand the term activation energy and represent it on a reaction profile

Particles will not necessarily react when they collide. They need to have enough energy to be able to react on collision (i.e. they need to hit one another hard enough).  The minimum energy required for particles to react on collision is called the activation energy.  Such collisions are called “successful collisions”.  The higher the activation energy the slower the reaction.

The diagrams below show the activation energy on both an endothermic and an exothermic reaction reaction profile. Note also the enthalpy change (∆H).