Determination of the Activation Energy

The sign of the activation energy E (or Ea) should be positive (endothermic).

For any reaction to occur, the reactants must obtain sufficient energy to overcome the energy barrier. Otherwise, the reaction does not occur. The minimum energy needed to overcome the energy barrier is called activation energy (Ea) of the reaction. Since energy must be absorbed to overcome the activation energy, the activation energy is thus endothermic (with a positive sign).