What is the enthalpy of solution for NaI and how is it calculated?

The enthalpy of solution for NaI can be calculated by using the formula:

Enthalpy of Solution (ΔH_sol) = Enthalpy of Hydration (ΔH_hydr) – Lattice Energy (ΔH_lattice)

Given that the lattice energy of NaI is 686 kJ/mol and the enthalpy of hydration is 694 kJ/mol, we can substitute these values into the formula:

ΔH_sol = 694 kJ/mol – 686 kJ/mol = 8 kJ/mol

Thus, the enthalpy of solution for NaI is +8 kJ/mol.

This enthalpy change applies to the process of dissolving solid NaI in water. When NaI is added to water, the solid crystal lattice must be broken apart to allow Na⁺ and I^– ions to disperse in the solution. The lattice energy represents the energy required to dismantle the ionic lattice, while the enthalpy of hydration represents the energy released when these ions are surrounded by water molecules. Since the enthalpy of hydration is greater than the lattice energy in this case, the process is slightly endothermic, resulting in a net positive enthalpy change.