How can the law of conservation of mass apply to a burning log, if all that remains of it is ash?

Question

A.
The ash has the same mass as the log, although a large percentage of it blows away.

B.
The law of conservation of mass applies to changes of state but not to chemical reactions.

C.
The law of conservation of mass applies to substitution and displacement reactions, but not to combustion reactions.

D.
The masses of the gases released into the air plus the mass of ash equal the mass of the log before burning.

Answer 1

The correct option is:

D. The masses of the gases released into the air plus the mass of ash equal the mass of the log before burning.

The law of conservation of mass states that mass cannot be created or destroyed in a chemical reaction. In the case of a burning log, while it appears that the log has disappeared, what actually happens is that the mass of the log is transformed into other substances, such as ash and gases (like carbon dioxide and water vapor), which are released into the air. If you account for the mass of the ash and the gases produced, their total mass will equal the original mass of the log.