Increases from Be to Ba The reactivity of alkaline metals with water increases down the group. The reactions become easier as the energy needed to form positive ions falls. This is due to decrease in ionization enthalpy down the group. This leads to lower activation energies, and therefore faster reactions. Mg+H2O(g) → MgO+H2 Ca+H2O → Ca(OH)2+H2 Hence reactivity increases from beryllium (Be) to barium (Ba).