What is Activation Energy

Activation energy, in simple terms, is the energy required for a chemical reaction to take place. Introduced by Svannte Arrhenius, a Swedish scientist in 1889, it is also described as the energy that must be overcome so as to have a chemical reaction. It is given in kilojoules per mole and denoted by Ea.

Many molecules in nature can coexist peacefully without any reactions. However, some will react when placed together, mildly or very vigorously. The molecules have to be very close to each other and in a specific orientation for any reaction to take place. In such a case, some kind of energy is needed to break pre-existing bonds and create new ones in the chemical reaction; this energy is the activation energy.

The strength of the existing bonds will determine the amount of energy needed for the reaction to take place, this amount of energy is known as the energy barrier. The collision of the molecules rarely provides enough energy for most reactions therefore other sources are needed to start the reactions. Among the sources are physical factors like heat and chemical factors for example appropriate enzymes, these will activate the molecules enough to begin reacting.

As long as the reaction is set in motion it will release additional energy, especially heat that will activate the next reaction therefore no more need to add energy. A good example is firewood and fire, once ignited, it activates the next and the fire goes on unabated.

 Adding heat to most reactions will speed them up, however in biological reactions, there is a limit since too much heat will damage the cells. In order to initiate and accelerate these reactions, enzymes are used to lower the activation energy of specific reactions. Enzymes are biological catalysts made of protein and acts in lowering the energy needed for a reaction to enter the transition state.

Enzymes facilitate reactions but do not undergo any change themselves; they align molecules strategically for reactions to take place by their unique shapes for specific reactions. With the use of these catalysts, reactions will take place at lower temperatures therefore protecting the cells from damage. A good example is glucose and oxygen in the metabolism in the cell. These two molecules will coexist without ever reacting, but with the right enzyme, they will react to produce the energy required by the body.

Importance of activation energy

  • Without this energy barrier, chemical instability would increase and catastrophic events can be prone to occur.
  • It provides a stable environment for all living organisms.
  • It is the safeguard between necessary chemical reactions and stability of the environment we live in.


Activation energy exists mainly to keep dangerous reactions at a minimum for the maintenance of a stable environment. The bonds in the elements or compounds are stronger before a reaction, the higher the activation energy.