Definitions you need to know - Solubility -Entropy: how far?

Lattice Energy is the enthalpy change (energy released) when one mole of an ionic solid is formed from its constituent gaseous ions infinitely far apart.

X^a+ _(g) +Y^b- _(g) → X_bY_{a (s)}   ΔH _lattice

Enthalpy change of hydration is the enthalpy change (energy released) when one mole of gaseous ions dissolved in sufficient solvent to given infinity dilute solution.

X^a+ _(g) + aq → X^a+ _(aq)     ΔH_hyd (X^a+)

Y^b- _(g) + aq→ Y^b- _(aq)      ΔH_hyd (Y^b-)

Enthalpy change of solution is the enthalpy change when one mole of a compound is dissolved in sufficient solvent to give an infinitely dilute solvent.

X_bY_{a (s)} + aq→ X_bY_{a (aq)}  

ΔH _solution =  -ΔH _lattice + ΔH_hyd (X^a+) + ΔH_hyd (Y^b-)

An Infinitely dilute solvent is a solution in which further dilution does not cause a heat change.