Question

Ammonium chloride, when dissolved in water, leads to a cooling sensation. The dissociation of $N{{H}_{4}}Cl$ at constant temperature is accompanied by:
A) Increase in entropy
B) Decrease in entropy
C) No change in entropy
D) No change in enthalpy

Answer 1

Hint: Entropy tells the randomness of the molecules. The cooling sensation of the dissolution of ammonium chloride in water is due to the fact that the reaction is endothermic, which means that the enthalpy of the reaction increases. If the product has more elements then the randomness will increase.

Complete answer:
There are many properties of the reaction that can tell the nature of the reaction. These are Gibbs free energy, enthalpy, entropy, etc. Enthalpy is the change in the heat of the reaction, and entropy is the randomness of the molecules.
So, in the question, the reaction is between ammonium chloride in water. The formula of ammonium chloride is $N{{H}_{4}}Cl$ and this is a salt made up of cation and anion. When it is dissolved in water, then there is a dissociation of ions. The reaction is given below:
$N{{H}_{4}}Cl+{{H}_{2}}O\to NH_{4}^{+}+C{{l}^{-}}$
The cooling sensation of the dissolution of ammonium chloride in water is due to the fact that the reaction is endothermic, which means that the enthalpy of the reaction increases.
So, as we can see that the number of ions increases when the ammonium chloride is dissolved in water which means that the randomness increases. As the randomness increases, the entropy increases.

Therefore, the correct answer is an option (A)- Increase in entropy.

Note:
If the reaction takes place without any external factor and there are decreases in the temperature then the value of enthalpy is positive and when there is an increase in the temperature then the value of enthalpy is negative.