Magnesium reacts vigorously with hot water

“Rate of a reaction process depends on the energy level of its reactants and it is found that the energy of reactants are much higher at high temperatures. Higher energy levels means much faster reaction rates. This coupled with other factors means, the reaction of magnesium with hot water or steam is much higher compared to cold water.”

       Magnesium is an element belonging to the s-block in the periodic table. Compared to transition elements or d-block elements (eg iron, copper etc), s-block elements or rare earth elements are highly reactive. Magnesium reacts with water to produce white magnesium hydroxide and hydrogen gas.                      Mg(s) + 2H2O(l) —> Mg(OH)2(s) + H2(g)
       Magnesium reacts violently with steam giving an intense white light.
       Under usual conditions, magnesium is covered with an insoluble layer of magnesium oxide (MgO) due to its exposure to surrounding air. This magnesium oxide makes it less reactive with water. The kinetic energy of the reactants influences the rate of the overall reaction. This means that the chemical reaction takes place only when the reactants posses a minimum amount of energy called activation energy. And the kinetic energy of the reacting species increases with a rise in temperature, which means magnesium reacts faster and more vigorously in hot water and steam. In cold water, the reacting species do not receive the necessary activation energy, more over the magnesium is covered by a layer of oxide layer, which the cold water is unable to disturb. There also are other factors which influence the reaction rate.
       Before the formation of hydrogen molecules, the hydrogen atoms produced during the reaction are initially adsorbed on the surface of the magnesium metal. This layer of hydrogen atoms tend to inhibit the reaction and these hydrogen atoms get their required electrons from the magnesium metal for thier formation of hydrogen molecules. Higher temperature means that the inter atomic bonds of magnesium weakens and electrons are released much more easily to the hydrogen atoms. Therefore the reaction tends to take place easily with hot water or steam than cold water.
       In addition at higher temperatures, the hydrogen atoms are not effectively adsorbed on the surface of the magnesium metal and therefore the metal is continuously exposed to the attack by hot water. Moreover at high temperatures water molecules are ionized which means, the hydrogen ions are more easily available for the formation of hydroxyl ions which easily results in the formation of magnesium hydroxyl, thereby making reaction of magnesuim with hot water and steam much more violent and vigorous.

References


[1] http://sciencepark.etacude.com/lzone/reactivity/Mg.php
[2] http://www.elementalmatter.info/magnesium-reaction.htm
[3] http://www.hindu.com/seta/2006/02/16/stories/2006021600651600.htm