7.15 - Activation energy
Learn what activation energy means, why a collision may fail to produce a reaction, and how the energy barrier is represented on a reaction profile.
The minimum energy for reaction
Reactant particles must collide in a suitable way to react. A collision can fail even when the particles meet: they may not have enough energy to reach the higher-energy state through which the reaction proceeds.
Activation energy
Activation energy is the minimum energy that reacting particles must have for a chemical reaction to occur.
Particles colliding with less than this energy remain as reactants. With sufficient energy, a suitable collision can form products. The energy helps overcome the barrier to rearranging bonds; it is not energy released by the reaction.
Even an exothermic reaction can need a spark or flame to begin. Its overall release of energy does not remove the initial barrier. Once started, the energy released may enable further particles to react.
Locating the barrier
A reaction profile shows relative energy as reactants become products. The energy barrier is the climb from the reactants' energy level to the highest point on the pathway.
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