Question

Which ion liberates most energy on hydration?

Answer 1

• Hydration enthalpy ($∆H_{hyd}$) is the change in enthalpy when one mole of gaseous ions is dissolved in a particular amount of water under standard conditions to make it a dilute solution.
• Hydration enthalpy generally decreases with increase in size of the ion and so while moving from top to bottom in a group or left to right in a period, hydration enthalpy decreases.
• Thus the ions which are smaller in size have higher hydration enthalpy. ${\mathrm{Li}}^{+}$liberates the most energy among all the elements upon hydration, forming a cage like structure surrounded by water molecules.