Question

The dissolution of ammonium chloride is an exothermic process. If true enter 1 else 0.
(A) 0
(B) 1

Answer 1

The molecular formula of ammonium chloride is ${\text{N}}{{\text{H}}_{\text{4}}}{\text{Cl}}$. We know that means ammonium chloride will dissociate into its constituent ions. The reaction in which heat is released or given out is known as an exothermic reaction. When an exothermic reaction occurs, the system feels hot.

Complete Step by step answer: When ammonium chloride dissolves in water it dissociates into ammonium ion $\left( {{\text{NH}}_4^ + } \right)$ and chloride ion $\left( {{\text{C}}{{\text{l}}^ - }} \right)$ and the system feels colder. The dissolution reaction of ammonium chloride is as follows:
${\text{N}}{{\text{H}}_{\text{4}}}{\text{Cl}} \rightleftharpoons {\text{NH}}_4^ + + {\text{C}}{{\text{l}}^ - }$
During this transformation of ammonium chloride from solid to liquid the entropy increases and the change in entropy is positive.
We have an equation,
$\Delta G = \Delta H - T\Delta S$
Where, $\Delta G$ is the Gibbs free energy change,
$\Delta H$ is the enthalpy change,
$T$ is the temperature,
$\Delta S$ is the entropy change.
As the entropy change during dissolution of ammonium chloride is positive. The term $T\Delta S$ becomes positive.
Thus, the value of $T\Delta S$ is greater than $\Delta H$. Thus, the value of $\Delta G$ becomes negative.
Also, the dissolution of ammonium chloride is a spontaneous process. Thus, $\Delta G$ is negative.
The value of the enthalpy change i.e. $\Delta H$ for the dissolution reaction of ammonium chloride is $+ 15.1{\text{ kJ mo}}{{\text{l}}^{ - 1}}$.
A positive value of $\Delta H$ indicates that the dissolution reaction of ammonium chloride is an endothermic process. In an endothermic process, heat is absorbed. Thus, $\Delta H$ is positive.
Thus, the statement ‘the dissolution of ammonium chloride is an exothermic process’ is not true.

Thus, the correct option is (A) 0.

Note: A negative value of $\Delta H$ indicates that the reaction is an exothermic process. In an exothermic process, heat is released or given out. For an endothermic process, the value of $\Delta H$ is positive. In an endothermic process, heat is absorbed and the system feels cold.