In class we are currently learning about equilibrium and Le Chateliers principal. The principal makes sense but seems contrary to some other concepts. For example, using stoichiometry to calculate the mass of reactants for a certain amount of products. If we know the reaction is always going to equilibrium where the forward and reverse reactions are happening at the same rate, then how will the reaction ever be "complete" because according to the principal even if the reaction were to be complete and all the reactants were gone, the reverse reaction should be occurring. This is not the case in reactions like burning magnesium.
I'm guessing that not all reactions are reversible and that the principal is correct but in some cases it would take a long time to reach equilibrium.