Question

What is threshold energy?

Answer 1

We come across the term threshold energy in chemical kinetics. There is a difference between threshold energy and energy of activation. Students must not confuse both these terms: Threshold Energy and Activation Energy. Threshold Energy is the minimum energy needed for a reaction to occur.

Complete step by step answer:
1: Threshold Energy is the minimum Kinetic Energy the molecules must have to bring about effective collisions between two reactant molecules which are considered as spheres, thus resulting in a chemical reaction between the two reactants.
2: Thus, we can write:
Threshold Energy = Average of the initial Kinetic Energy of reactants + Activation Energy (${E_a}$)
3: In case the reactants at the initial state (start of the reaction) have sufficient energy for the collisions, then the threshold energy is equal to Activation Energy. (${E_a}$)
4: Molecules that have a Kinetic Energy equal to or higher than the Threshold Energy will react.

Note:
Students must go through the Chemical Kinetic chapter for a better understanding of the reaction proceeding. Also, do not confuse the terms internal energy and threshold energy. They are interconnected, but different. Students should always be clear about these terms and concepts.
The average internal energy is the energy that your reactant molecule has internally. The threshold energy is the energy that these molecules must have in order for a reaction to take place. The difference between these two values is the activation energy, (${E_a}$). The activation energy is the energy barrier that a molecule must overcome for the reaction to take place.