ThermochemistryMedium
Question
The lattice energy of solid NaCl is 180 kcal/mol. The dissolution of the solid in water, in the form of ions is endothermic to the extent of 1kcal/mol. If the solvation energies of Na+ and Cl– ions are in the ratio 6:5, then what is the enthalpy of hydration of sodium ion?
Options
A.−85.6 kcal/mol
B.−97.6 kcal/mol
C.82.6 kcal/mol
D.100 kcal/mol
Solution
$\Delta_{\text{Lattice}}H + \Delta_{\text{Hydration}}H = \Delta_{\text{Solution}}H$
$\text{Or, }180 + (6x + 5x) = 1 \Rightarrow x = - 16.27\text{ kcal/mol} $$$\therefore\Delta_{\text{Hyd}}H_{Na^{+}} = 6x = - 97.64\text{ kcal/mol}$$
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