Question

Threshold energy of the reaction is (in kJ):

Answer 1

Hint: Molecules require a certain amount of energy to take part in a chemical reaction. This energy can be provided by heating or doing some work on the molecules.

Complete step by step solution: Let’s see what threshold energy is:
-Reactant molecules require a minimum amount of energy to get converted into the products at the completion of the reaction,
-Threshold energy is the minimum amount of the energy required by the reacting molecules for a reaction to take place.
-Molecules that have energy greater than or equal to threshold energy take part in the completion of the chemical reaction.
-This energy is required for the molecules to have greater number of collisions. More the number of collisions faster will be chemical reaction.
So, we have seen that molecules taking part in a chemical reaction are those which cross the energy barrier. This barrier is crossed by having sufficient or more threshold energy.
-Threshold energy can be expressed in many units like joules, kilo joules, etc.
Hence, the final answer is:
The minimum energy required by the molecules in kilojoules (kJ) for a reaction to take place is called threshold energy.
Let us take an example to understand threshold energy.

\[NO\,+\,{{O}_{3}}\,\to \,N{{O}_{2\,}}\,+\,{{O}_{2}}\]

Now, in this reaction a molecule of nitrogen monoxide reacts with a molecule of ozone to give nitrogen dioxide and oxygen gas as products. For the reaction to occur the molecules of ${{O}_{3}}$ and NO should have sufficient energy to cross the energy barrier and then to form the products. If the molecules will not have sufficient threshold energy then effective collisions will not take place and the reaction will not occur.

Note: The energy of the reactants is higher than the energy of products. Threshold energy is equal to the sum of the energy of the reactants and activation energy.