An equation for the reaction of:
(i) iron with stream-
When a metal reacts with steam then the products formed are metal oxide and hydrogen gas.
Metal + steam → Metal oxide + Hydrogen
When red hot iron reacts with steam to form iron(II,III) oxide and hydrogen:
3Fe(s) + 4H2O(g) steam → Fe3O4 (s) + 4H2(g)
(ii) calcium with water:
When a metal reacts with water( cold water or hot water) then the products formed are metal hydroxide and hydrogen gas.
Metal + steam → Metal hydroxide + Hydrogen
Calcium reacts with cold water to form calcium hydroxide and hydrogen gas:
Ca(s)+ 2H2O(l) → Ca(OH)2(aq) + H2(g)
(iii) potassium with water:
Potassium reacts violently with cold water to form potassium hydroxide and hydrogen gas:
2K(s)+ 2H2O(l) → 2KOH(aq) + H2(g) + heat.
In this reaction so much heat is produced get hydrogen gas formed catches fire and burns explosively.