How does the law of conservation of mass apply when wax appears to disappear as a burns?

Answer 1

Solid wax, a hydrocarbon, burns in oxygen (from the air) to produce invisible carbon dioxide and water (steam). So you see the wax disappear in a flame but don't notice the equivalent mass of hot gasses rising up.

Weight of candle before lighting = 50g say.

Weight the gases (not easy!) after candle completely gone = 50g.

Compare and contrast the nuclear fission or a Uranium candle.

Weight of candle before 'lighting' = 50g

Weight of all products of nuclear fission after candle (and most likely your laboratory, street, town etc) has completely gone = 49.999g (or something).

Where has the 0.00001g gone? An awful lot of heat.

Answer 2

The law of conservation of mass states that mass cannot be created or destroyed in a chemical reaction, only rearranged. When wax burns, it undergoes a chemical reaction with oxygen to produce carbon dioxide and water vapor. The mass of the wax is conserved in the products of the reaction, even though it may appear to disappear as it is converted to gas and ash.

Answer 3

Because the wax is consumed - ie. oxidzed. It is converted by chemical reaction to gasses and soot (carbon).