Chapter 13, Problem 13.28P

(a)

Interpretation Introduction

Interpretation:

Whether the dissolution of ${\text{NH}}_4\text{Cl}$ exothermic or endothermic is to be determined.

Concept introduction:

The enthalpy is the thermodynamic property of the system. It is defined as the sum of internal energy and the product of pressure and volume of the system. It is a state function and is independent of the path followed by the system from initial to the final state. It is an extensive property. The total enthalpy of the system can not be measured directly so the change in enthalpy $\left(\Delta H\right)$ is measured. If $\Delta H$ of the reaction is positive, it is an endothermic reaction and if $\Delta H$ of the reaction is negative, it is an exothermic reaction.

(b)

Interpretation Introduction

Interpretation:

Whether $\Delta H_{\text{lattice}}$ for ${\text{NH}}_4\text{Cl}$ larger or smaller than the combined $\Delta H_{\text{hydration}}$ of its ions is to be determined.

Concept introduction:

The enthalpy change of hydration is the enthalpy change when one mole of the ionic species is dissolved in water to give a solution of infinite dilution. It is represented by $\Delta H_{\text{hydration}}$. It is always negative.

The lattice energy is the amount of energy released when the constituent ions are combined to form a compound. It is always negative.

(c)

Interpretation Introduction

Interpretation:

The reason for the dissolution of ${\text{NH}}_4\text{Cl}$ in water is to be determined.

Concept introduction:

Solubility is the chemical property of any substance due to which it dissolves in other substances. It is measured in terms of the maximum amount of solute that can be dissolved in the given amount of solvent. It depends on the intermolecular forces. The stronger the intermolecular forces, the higher will be the solubility.