What does enthalpy of solution mean?

Answer 1

Enthalpy of solution describes the net change in heat when a solute is dissolved in a solvent. Specifically, the standard enthalpy of solution is the heat change when one mole of solute is completely dissolved in a solvent to form a solution concentration of 1 mol per dm3 under standard conditions.

The net change in heat can be broken down into the sum of two heats. First, the solute crystals must break from their lattice. This is known as the lattice enthalpy and its reversal is typically endothermic. Second, the ions are solvated (or hydrated in the case of aqueous solutions), which is typically an exothermic step. Depending on the magnitude of each of these factors, the sum can lead to a positive or negative enthalpy of solution.