The energy required to initiate an exergonic reaction is called

energy of activation is the correct answer.

Explanation:

All the chemical reactions including an exothermic reaction require activation energy to initiate a reaction. Activation energy is the minimum amount of energy required to activate the molecules to the situation that they can experience a chemical change. If the activation energy is lower the faster the reaction occurs. Joules, kilocalories/mol, kilojoules per mole are the units for activation energy.