The reactions of Na and Mg with water

• Reaction of sodium with water: Explanation

  Sodium metal reacts vigorously with water, the reaction is very exothermic. 

  Sodium floats on the water, it moves about the surface of the water and fizzes. The metal melts to form a silvery ball, eventually disappearing and the solution remaining is colourless. The solution contains sodium and hydroxide ions, making it alkaline. 
• Reaction of sodium with water: Equation

  $2Na+$$2H_2O\ \rightarrow\ 2NaOH+$$H_2$
• Reaction of magnesium with water: Explanation

  Magnesium metal reacts very slowly with water. The remaining solution contains magnesium and hydroxide ions, making it slightly alkaline.
• Reaction of magnesium with water: Equation

  $Mg+$$2H_2O(l)\ \rightarrow\ Mg\left(OH\right)_2+$$H_2$
• Reaction of magnesium with steam: Explanation

  Magnesium reacts vigorously with water vapour at temperatures above 100°C in the absence of air. The magnesium burns with a bright white light and a white solid is formed. 
• Reaction of magnesium with steam: Equation

  $Mg+$$H_2O(g)\ \rightarrow\ MgO+$$H_2$