# What's the actual or official definition of activation energy? [duplicate]

In some sources I have seen that activation energy is the minimum energy required to cause a reaction. This implies that activation energy doesn't change with temperature (not considering very high changes). In other sources it is the difference between the energy required to cause the reaction & the energy of the reactants. This implies that activation energy is temperature dependent since the energy of the reactants change with temperature. So which is correct? Also another source (khan academy's guardian chemist) says that "The official definition of activation energy is a bit complicated and involves some calculus."

Activation Energy is the minimum amount of energy needed extra than the average potential energy of the reactants to cause a reaction.And it does not change with the change of temperature, and for clarification the energy of the reactant molecules don't also change with the reaction. It is just the rate which changes with the reaction according to the arrhenius equation k=Ae^{-\frac{Ea}{RT}}So,the fraction of molecules having energy higher than activation energy changes with change in temperature. I think the easier definition can be stated like this

• The free energy of activation depends on temperature. Free energy has enthalpy and entropy components, and the entropy component is multiplied by the temperature. – diogom Feb 5 '18 at 19:12
• The FREE ENERGY ($\Delta$ G) and ACTIVATION ENERGY both are different.The FREE ENERGY change is of total reaction but ACTIVATION ENERGY is only regarding min energy which is independent of temperature. Don't combine them without any logic.. Think twice before adding comments and downvoting. – Soumik Das Feb 5 '18 at 19:42
• Actually both exist: there is the free energy of reaction ($\Delta G$) and also the free energy of activation ($\Delta G ^{\ddagger}$). – diogom Feb 5 '18 at 23:24
• Free Energy (e.g. Gibbs) is different from Energy. The Arrhenius equation considers Energy and not Free Energy. In that regard, what you wrote is correct, Energy does not depend on temperature. However, free energy depends on temperature. – diogom Feb 5 '18 at 23:33