Question

What is the principle of atomic conservation? Explain with an example.  

Answer 1

Law of conservation of mass is always valid in all chemical changes. Mass of substances is due to the atoms of the elements. Therefore in chemical reaction atoms of all elements which constitute the reactants and products are conserved, so moles of atoms are also conserved. This is known as principle of atomic conservation. This principle is helpful in solving problems of nearly all stoichiometric calculations. 

For Example: 

KClO_3(s) → KCl_(s) + O_2(g) 

Applying POAC for K atoms 

Moles of K atoms in KClO₃ = Moles of K atoms in KCl 

Since one mole of KClO₃ contains 1 mol of K atom. 

Similarly 1 mol of KCl contains one mole of K atoms. 

(Mass-mass relationship) 

Applying POAC for ‘O’ atoms 

Moles of O atom in KClO₃ = Moles of O atom in O₂ 

(Mass volume relationship of reactant and product) 

In this way applying POAC we can break the chemical equation into a number of arithmetic equations without balancing the chemical equation. Moreover number of reactions and their sequence from reactants to products are not required. It is important to note that POAC can be applied for the atoms which remain conserved in chemical reaction.

Notes: 

1. The balanced reaction is essential in Mole method of solving. Only while using POAC (which would be applicable only in certain cases), balanced reaction is not required. 

2. POAC can be used for all atoms in the compound only IF all the reactants and products are known or it can be applied to those elements for which it is known that its atoms are conserved.