Question

Anhydrous $Al{Cl}_3$ is covalent. From the data given below, predict whether it would remain covalent or become ionic in aqueous solution.

Given : Ionization energy for $Al{Cl}_3=5137$ kJ mol ${}^{-1}$, ${\Delta }_{Hydration}$ for ${Al}^{3+}=-4665$ kJ mol${}^{-1}$, ${\Delta }_{Hydration}$ for ${Cl}^{-}=-381$ kJ mol${}^{-1}$.

• A. $-340$ kJ/mol
• B. $-290$ kJ/mol
• C. $91$ kJ/mol
• D. $-671$ kJ/mol

Answer 1

Answer: (D)

$-671$ kJ/mol

The enthalpy change $\Delta H$ for the reaction $Al{Cl}_3+\left(aq\right)⟶Al{Cl}_3\left(aq\right)$ is :

$\Delta H=$ Energy released during hydration - Energy used during ionization

$=\left[\right(-4665)-(3\times 381\left)\right]+5137=-5808+5137=-671$ kJ/mol

Since the Energy released during hydration is greater than the Energy used during ionization, $AlC{l}_3$ will become ionic in aqueous solution.