Question

What is the hydration enthalpy of alkali metals?

Answer 1

Hydration enthalpy:

1. Hydration enthalpy is defined as the amount of heat released on the hydration of one mole of ions.
2. It is the measure of released energy when the interaction is set between the water molecules and positive or negative ions.
3. The size of hydration enthalpy depends on the attraction between the water molecules and ions.

Hydration enthalpy of alkali metals are:

1. In the periodic table, hydration enthalpy decreases from top to bottom as the ionic size of the cation molecules increases.
2. The highly charged ions have a high enthalpy of hydration because they have more cations. For example, Magnesium has a high enthalpy as compared to Sodium.
3. The order of hydration enthalpy is ${\mathrm{Li}}^{+}(506\mathrm{kJ}/\mathrm{mol})>{\mathrm{Na}}^{+}(406\mathrm{kJ}/\mathrm{mol})>{\mathrm{K}}^{+}(330\mathrm{kJ}/\mathrm{mol})>{\mathrm{Rb}}^{+}(310\mathrm{kJ}/\mathrm{mol}),{\mathrm{Cs}}^{+}(276\mathrm{kJ}/\mathrm{mol})$.