Question

Lattice energy of NaCl is $-186$ kcal/mol. If solution enthalpies of Na$+$ and Cl${}^{-}$ are $-97$ kcal/mol and $-85$ kcal/mol respectively. The enthalpy NaCl solution in kcal will be:

• A. $-4$
• B. $182$
• C. $368$
• D. $4$

Answer 1

The correct option is D $4$

The enthalpy of solution of NaCl in kcal is:

$\Delta H_{solution}=\Delta H_{\text{solution of cation}}+\Delta H_{\text{solution of anion}}-\Delta H_{\text{Lattice energy of NaCl}}$

$\Delta H_{solution}=(-97)+(-85)-(-186)=4$ kcal/mol

The enthalpy change of solution refers to the amount of heat that is released or absorbed during the dissolving process (at constant pressure). This enthalpy of solution (ΔHsolution) can either be positive (endothermic) or negative (exothermic).

Hence, the correct option is $D$