Enthalpy of Solution
The heat absorbed or released when one mole of a substance dissolves completely in a large excess of solvent.
Formula / equation
ΔH_sol = ΔH_lattice + ΔH_hyd
Unit
kJ/mol
In depth
The value is the small difference between two very large opposing terms: the endothermic breakup of the lattice and the exothermic hydration of the ions. A slight imbalance either way produces the familiar warming or cooling observed when salts dissolve.
Examples in the real world
NH₄NO₃ has ΔH_sol = +25.7 kJ/mol and chills the water; CaCl₂ at −82 kJ/mol makes it noticeably hot.