Please explain equivalent concept used to solve stoichiometry problem

Equivalent concept is similar to mole concept i.e in any chemical reaction the reactants react in same equivalents to give same equivalents of products.

BaCl₂+Al₂[SO₄]₃  --->BaSO₄ + AlCl₃
      a              b                   0              0 [Before reaction]
      0           b-a                   a               a  [after rection]

Where a and b are the number of equivalents. ( Number of equivalents = weight/(equivalent weight) )