Question

In a reaction, the threshold energy is equal to:
a.) activation energy + normal energy of reactants
b.) activation energy − normal energy of reactants
c.) normal energy of reactants − activation energy
d.) average kinetic energy of molecules of reactants

Answer 1

Hint: The threshold frequency in a chemical reaction is the minimum energy that molecules need to have for the reaction to take place and the difference between the threshold energy and internal energy (or normal energy that molecule has) is known as activation energy.

Complete step by step solution: The molecules that have the energy equal or the greater than the threshold energy, those molecules will be able to react in any reaction.
The activation energy is the energy at which molecules of the reaction are active enough to react with each other to form the products of the reaction. So, for the reaction to take place, activation energy is supplied to the molecules that don’t have enough energy to reach the threshold energy that molecules need for the reaction to take place.
Hence the activation energy is equal to the difference between the threshold energy and the normal energy of the reactants.
Hence activation energy = threshold energy - normal energy of the reactants
So, threshold energy= activation energy + normal energy of the reactants
Hence the threshold energy is the total sum of the activation energy and the normal energy of the reactants.
So, option (A) is the correct answer.

Note: So we see that the threshold energy is greater than the activation energy. This we will understand with the following interpretation
Let us have a molecule which is bound with an energy of ${\text{X}}$. Now if this molecule is given the same amount i.e. ${\text{X}}$ of energy, then it will be fully ready to split but to split it and make it move away, they will need greater energy.
Hence the threshold frequency is greater than the activation energy.