Question

How is threshold energy related to the activation energy of the reaction?

Answer 1

Activation energy may be defined as the excess energy that the reactant molecules (having energy less than the threshold energy) must acquire in order to cross the energy barrier and to change into the products.

Thus,

Activation Energy = Threshold energy − Average energy possessed by reactant molecules

or, \[\ce{E_a = E_{threshold} - E_{reactants}}\]

Threshold energy is the minimum total energy that the reacting species must possess for a chemical reaction to occur.