How does reaction of sodium and potassium with water differ from reaction of magnesium with water? Explain.
Metals at the top of the reactivity series (Sodium, potassium) react readily (violently) with cold water forming hydroxides with the liberation of H2, the heat evolved is sufficient for the hydrogen to catch fire.
Na(s) + 2H2O(l) → NaOH(aq) + H2(g) + large amount of heat energy
K(s) + 2H2O(l) → KOH(aq) + H2(g) + large amount of heat energy
While metals like Magnesium is less reactive towards cold water. It reacts very slowly with cold water. So, no fire is observed in this case.
Mg(s) + H2O(l) → Mg(OH)2(aq) + H2(g)