Hydration energy

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As hydration energy (including hydration energy or hydration enthalpy ), the energy called, which is released when water molecules to ions accumulate. It is a special case of solvation energy with water as the solvent . Dissolves z. B. a salt in water, the ions at the edge of the ion lattice are released from the lattice by water molecules and enveloped by them.

  • In the case of salts in which the hydration energy is greater than or equal to the lattice energy (overcompensation), the salt-water mixture is heated during dissolution ( exothermic reaction ). Example: anhydrous calcium (II) chloride (CaCl 2 ). Such salts are said to be readily soluble .
  • When calcium chloride hexahydrate (CaCl 2 · 6H 2 O) is dissolved, however, the solution cools down ( endothermic reaction ). The cooling is based on the fact that the lattice energy required to dissolve the salt is not completely covered by the hydration energy and the energy still required is taken from the thermal energy of the water.


  • Hans P. Latscha, Helmut Klein: Inorganic Chemistry: Chemistry Basics I . Springer, Berlin 2013, p. 161, ISBN 3-66205-759-X