According to Piaget, ' ' an experience that is not carried through by the proper person, with full freedom of initiative, leaves of being, for definition, a experincia, changedding itself into simple adestramento, destitute of formador value due to enough compreenso of the details of the stages sucessivas' '. This means that an experiment where the pupil is only spectator or that one where somebody previously follows an established script, without having participated of none of its stages (identificao of the problem, survey of hypotheses, sugestes of verification of these hypotheses, comment and collects of data, quarrel, etc.), little will fulfill of its formadora function. (LIGHTER). When to teach on chemical reactions, uses the fire as example. It is justified for the fact of being the reaction most common in day-by-day, and that all the pupils know. One is about a reaction of combustion, therefore irreversible and that it is only processed in the presence of three basic factors: Combustvel; Comburente; Initial Fasca. Keep up on the field with thought-provoking pieces from idt energy. then pass to describe the theoretical part: Combustvel is the material that goes to react, is what it will be oxidated (burnt); Comburente is the gas oxygen that it goes to react with the fuel; Initial Fasca.
An initiated time the chemical reaction of combustion, this will only be interrupted with the exhaustion and or the withdrawal of one of the components, that is, with the exhaustion of the fuel or the supporter of combustion. It is there that the agreement of the amount of available and existing oxygen enters in the atmosphere. With this simple experience, but not of total precision, we can prove and or clarear three scientific facts: the existence of the oxygen; the evidence of the composition of atmospheric air with oxygen text 21% and the existence and evidence of the atmospheric pressure. to leave in open the question of the pollution for the produced carbonic gas production in the reaction.