Question

The following reaction is an example for what type of thermal reaction? $Cl + Cl \to C{l_2}$
A) Endothermic reaction
B) Exothermic reaction
C) Either exothermic or endothermic
D) Neither exothermic nor endothermic

Answer 1

Hint: The two $Cl$ atoms here are free radicals. Bonded molecules are more stable than free radicals. Therefore they have less energy compared to free radicals indicating that the energy has been released during the reaction process. With this information, we can understand the type of thermal reaction.

Complete Step by step answer:
- In the reaction given to us, there is a bond formation between the two chlorine free radicals to form a single chlorine molecule. Now in this reaction, we know that the $C{l_2}$ molecule is much more stable than the individual $Cl$ free radicals due to the fact that the two chlorine atoms in $C{l_2}$ satisfy inert gas valency.
- The stability of a molecule or an atom is inversely proportional to the energy of the molecule or the atom. $stability \propto \dfrac{1}{{Energy}}$
- So, in the given reaction the energy of the product chlorine molecule is significantly lesser than that of the reactant chlorine free radicals. This shows us the fact that energy has been released in the reaction process and this energy will be released in the form of heat meaning that heat is released in the reaction process.

Therefore, the reaction is an exothermic reaction i.e. option B.

Additional information: The molecules in which the atoms have inert gas valency are highly stable and have low to zero energy. These types of molecules usually take up a lot of energy in order to break their bonds and are significantly easier to produce from their individual atoms.

Note: If the stability of the molecule is high, then the energy of the molecule would be less and if the stability of the molecule is low, then the molecule will have higher energy. This accounts to the fact that the product in this reaction has lesser energy than that of the reactants.