Question

Write equations for the reactions of (i) iron with steam (ii) calcium and potassium with water and (iii) potassium with water.

Answer 1

(i) Iron react with steam to form the metal oxide and hydrogen. 

3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g) 

(ii) The reaction of calcium with water is exothermic but the heat evolved is not sufficient for the hydrogen to catch fire. 

Ca(s) + 2H2O(l) → Ca(OH)2(aq) + H2(g) 

(iii) Calcium starts floating because the bubbles of hydrogen gas formed stick to the surface of the metal. Potassium react violently with cold water and its reaction is so violent and exothermic that the evolved hydrogen immediately catches fire. 

2K(s) + 2H2O(l) → 2KOH(aq) + H2(g) + heat energy

Answer 2

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.