Activation Energy
Definition and meaning of Activation Energy in chemistry.
Activation energy is the minimum amount of energy that colliding particles must have for a chemical reaction to occur. Represented by the symbol Ea and usually measured in kilojoules per mole (kJ/mol), it acts as an energy barrier that reactants must overcome to be converted into products.
In more detail
The idea was introduced by the Swedish chemist Svante Arrhenius in 1889, and the link between activation energy and reaction rate is described by the Arrhenius equation. This shows that even a small rise in temperature can sharply increase the fraction of particles with enough energy to react. On an energy profile diagram, the activation energy is the height of the 'hill' that separates the reactants from the products.
Key facts
| Symbol | Ea |
|---|---|
| SI unit | Kilojoules per mole (kJ/mol) |
| Described by | The Arrhenius equation |
| Field | Physical chemistry |
A mixture of gasoline vapor and air does not ignite on its own, but a spark supplies the activation energy needed to start combustion.
Frequently asked questions
Does a catalyst change the activation energy?
Yes. A catalyst provides an alternative reaction pathway with a lower activation energy, which speeds the reaction up. It does not change the overall energy of the reactants or products.
What happens to activation energy when the temperature rises?
The activation energy itself stays the same, but at a higher temperature more particles have enough energy to overcome it, so the reaction goes faster.