Mole concept:

The mole is defined as the amount of a substance containing as many atoms, molecules, ions, electrons or other elementry entities as there are carbon atoms in exactly 12 g of ¹²C.

N_A = 6.022 X 10²³

The following are the definitions of 'mole' represented in the form of equations:

(1) no. of moles of molecules/atoms =        weight in g     

                                                             molecular/atomic wt

(2) no. of moles of gases =                volume at NTP            

                                            standard molar volume (i.e. 22.4 L)

(3) no. of moles of entities =                  no. of entities                

                                           Avagadro constant (i.e. 6.022 X 10²³)

(4) no. of moles of solute = molarity X volume of solution in L

    no. of millimoles = molarity X volume of solution in mL

(5) For a compound M_xN_y, x moles of N = y moles of M

 Note: 1 mole is a fixed no. of particles but not a fixed weight.

Principle of Atom Conservation (POAC):

This principle states that the moles of atoms of an element are conserved throughout the reaction.

This means, moles of an element in reactants = moles of the element in products.

eg. CO + O₂ -----> CO₂

In this moles of C in CO = moles of C in CO₂

This means, moles of CO = moles of CO₂.

Similarly, for O,

moles of O in CO + moles of O in O₂ = moles of CO₂

Thus, moles of CO + 2(moles of O₂) = 2(moles of CO₂)

Advantages of Mole Method over other Methods:

(1) Balancing of chemical equations is not required in the majority of problems as the method of balancing the chemical equation is based on the principle of conservation of atom conservation.

(2) Number of reactions and their sequences, leading from reactants to products, need not be given.

Note: Whenever balanced chemical equation is given, mole method is very useful.

eg. 2KClO₃ -----> 2KCl + 3O₂

Thus, 2(moles of KClO₃) = 2(moles of KCl)

     3(moles of KClO₃) = 2(moles of O₂)

     3(moles of KCl) = 2(moles of O₂)