POAC stands for the principle of Atom conservation which is used to solve a chemical equation.
It is derived from the Law of conservation of mass.
Mass of atoms of an element in reactant = mass of atoms of an element in a product.
This principle is useful in solving problems of nearly all stoichiometric calculations, one need not balance the chemical equation if POAC is obtained.
Example: Potassium Perchlorate decomposition reaction can be considered:
Applying POAC for K atoms: Moles of K atoms in = Moles of K atoms in since one mole contains 1 mole of K atoms.
Therefore, POAC works on the principle of conservation of mass.