Because formed during combustion gaseous products! If all of them gather and weigh the total weight of residues candles and gaseous products will be MORE of the initial mass candles, because combustion is the accession of oxygen to the elements forming part of candles, with the destruction of the parent compounds and formation of these gaseous products of combustion (mainly carbon dioxide and water, and some of the products of incomplete combustion, such as carbon monoxide and soot!) ! The following answer You whip complete nonsense! Mass is transformed into energy ONLY when a NUCLEAR REACTION! Energy during combustion is generated by the thermal effect of CHEMICAL reaction of combustion, thus the total weight of substances (substances of candles and oxygen taken from the air)involved in these reactions, does not change! The law of conservation of mass of the substance it does not contradict!