Question

When ammonium chloride dissolved in water the temperature decreases. The energy change for the dissolution of ammonium chloride is $ 284{\text{ J }}{{\text{g}}^{ - 1}} $ ?

Answer 1

Hint: When we dissolve ammonium chloride in water the temperature of solution decreases or the solution becomes colder than earlier. Since the dissolution of ammonium chloride is an endothermic process. Also we will find the dissociation energy of ammonium chloride by using the energy change for the dissolution of ammonium chloride.

Complete Step By Step Answer:
It has been observed that when we add crystals of ammonium chloride to water then the temperature of the solution decreases. We can also say that by adding the ammonium chloride to water, the solution becomes colder than earlier. The ammonium chloride decomposes into its ions when it gets dissolved in water. It can be represented as:
 $ N{H_4}Cl{\text{ }} \to {\text{ N}}{{\text{H}}_4}^ + {\text{ + C}}{{\text{l}}^ - } $
The reaction between the ammonium chloride and water is an endothermic reaction. Thus the solution becomes colder when we add ammonium chloride to water. The solute ammonium chloride absorbs the heat from solution and thus decreases the temperature of solution.
The energy of dissociation of ammonium chloride can be calculated as:
 $ \Rightarrow {\text{ }}\Delta {H_{diss.}}{\text{ = 284 J }}{{\text{g}}^{ - 1}}{\text{ }} \times {\text{ Molar mass of N}}{{\text{H}}_4}{\text{Cl}} $
 $ \Rightarrow {\text{ }}\Delta {H_{diss.}}{\text{ = 284 J }}{{\text{g}}^{ - 1}}{\text{ }} \times {\text{ }}\left( {14 + \left( {4 \times 1} \right) + 35} \right){\text{ g}} $
 $ \Rightarrow {\text{ }}\Delta {H_{diss.}}{\text{ = 284 J }}{{\text{g}}^{ - 1}}{\text{ }} \times {\text{ }}\left( {14 + 4 + 35} \right){\text{ g}} $
 $ \Rightarrow {\text{ }}\Delta {H_{diss.}}{\text{ = 284 J }}{{\text{g}}^{ - 1}}{\text{ }} \times {\text{ 53 g}} $
 $ \Rightarrow {\text{ }}\Delta {H_{diss.}}{\text{ = 15052 J}} $
 $ \Rightarrow {\text{ }}\Delta {H_{diss.}}{\text{ = 15}}{\text{.05 }} \times {\text{ 1}}{{\text{0}}^3}{\text{ J}} $
Therefore the energy of dissociation of ammonium chloride in water is $ {\text{15}}{\text{.05 }} \times {\text{ 1}}{{\text{0}}^3}{\text{ J}} $ . We can also represent in terms of kilo-joule as $ {\text{15 kJ}} $ . The energy is calculated per mole of ammonium chloride thus its units will be $ {\text{15 kJ mol}}{{\text{e}}^{ - 1}} $ .

Note:
The molar mass of ammonium chloride may vary as we have not taken decimal values of mass of chlorine. The molar mass is the mass of the compound for one mole of substance and it is calculated by taking the algebraic sum of atomic mass of all elements of the compound. The reaction between ammonium chloride and water is endothermic in nature.