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 answer 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 is neither created nor destroyed in a chemical reaction. When a log burns, it undergoes a chemical reaction (combustion), which converts it into ash, gases (like carbon dioxide and water vapor), and other byproducts. If you account for the mass of the gases released along with the mass of the ash that remains, the total will equal the mass of the original log, thereby demonstrating the law of conservation of mass in this context.