Standard enthalpy change of hydration

The standard enthalpy change of hydration, ΔHhydo, is the change in enthalpy when one mole of an ion in the gaseous state dissolves in water to form an infinitely dilute solution under standard conditions. This means that we need to dissolve the solute in excess water until there is no change in the energy absorbed or released by the system.

Some examples are:

Zn^{2+}(g)\rightarrow Zn^{2+}(aq)\; \; \; \; \; \; \; \Delta H_{hyd}^{\: o}=-2046\: kJmol^{-1}

ClO_4^-(g)\rightarrow ClO_4^-(aq)\; \; \; \; \; \; \; \Delta H_{hyd}^{\: o}=-238\: kJmol^{-1}

The standard enthalpy of hydration is always exothermic (negative) and increases (more negative) for ions with higher charge densities, i.e. higher charge-to-radius ratios.


Next article: Standard enthalpy change of solution
Previous article: Standard enthalpy change of electron gain
Content page of intermediate chemical energetics
Content page of intermediate chemistry
Main content page

Leave a Reply

Your email address will not be published. Required fields are marked *