Wed January 02, 2013 By: Avani Pandey

why does hydration enthalpy of alkali metals decrease with increase in size ? what is the explanation at the level of electrons and atomic configuration ?

Expert Reply
Thu January 03, 2013

It is the amount of energy released when one mole of gaseous ions combine with water to form hydrated ions.

M+ (g) + aq ? M+ (aq) + hydration energy

X- (g) + aq ? X- (aq) + hydration energy              


Higher the hydration energy of the ions greater is the solubility of the compound in water.

Further the extent of hydration depends upon the size of the ions. Smaller the size of the ion, more highly it is hydrated and hence greater is its hydrated ionic radius and less is its ionic mobility (Conductance).

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