Question

what is hydration energy?

Answer 1

here you go:
http://www.science.uwaterloo.ca/~cchieh/cact/applychem/hydration.html

Answer 2

in simple words
The energy released in the process of hydration is known as hydration energy.
Hydration:The process of dissolving a species in water is known as hydration.

Answer 3

Hydration is the process that happens after ionization.

When you dissolve a salt, the ions are first separated.
This process is endothermic.

THEN, they are hydrated, that means that water molecules surround them and the 'lone' ions become hydrated ions with the state symbol (aq).
I think this process is always exothermic. @Kryten will correct me if I'm wrong.

The net process is the dissolution itself, which can be either endothermic or exothermic, depending whether separation needs more energy than hydration provides or not.

Answer 4

yes that is correct @Vincent-Lyon.Fr

Answer 5

There is one additional thermodynamic step, which is the creation of the holes for the ions in the solvent. This involves pulling apart the solvent molecules, and is also always endothermic. This step is crucial to the overall thermodynamics, however, because the endothermicity of this step explains why dissolving nonpolar solutes in polar solvents is difficult. You don't recover through hydration enough energy to compensate for the disruption of favorable interactions between solvent molecules.