You and your friend are sitting around a campfire and he notices that the ashes that are left after all of the wood has burned seem significantly less than the amount of wood that was originally put into the fire. He indicates that surely the amount of substance after the reaction (the burning of the wood) is less than the amount of substance before the reaction. Explain the misconception in your friend's conclusion and how this situation relates to the law of conservation of matter.

Answer and Explanation:

My friend's conclusion would break the law of conservation of matter, according to which, in any closed system, the mass of the system remains constant. He is right in his observation that the ashes of the wood seem significantly less than the amount of wood put into the fire. What he is not taking into consideration is that mass cannot be destroyed just like that. The rest of the mass of the wood, while burning, became CO2 and H2O. Thus, even though we cannot see it like we can see the ashes, the original mass has been maintained.

Burning and other changes in matter do not destroy matter. The mass of matter is always the same before and after the changes occur.

The law of conservation of mass states that matter cannot be created or destroyed.

The law of conservation of mass states that, for any closed system, the mass of the system must remain constant.

So, in other words, mass cannot be created nor destroyed.

In a burning log, the initial mass of the wood and the ashes that are left behind after it burns are different, which would seem to violate the law of conservation of mass.

However, the rest of the mass is actually in the form of

C

O

2

and

H

2

O

that were also produced as the log burned

Explanation:

It may seem as though burning destroys matter, but the same amount, or mass, of matter still exists after a campfire as before. It shows that when wood burns, it combines with oxygen and changes not only to ashes but also to carbon dioxide and water vapor. The gases float off into the air, leaving behind just the ashes. Suppose you had measured the mass of the wood before it burned and the mass of the ashes after it burned. Also suppose you had been able to measure the oxygen used by the fire and the gases produced by the fire. What would you find? The total mass of matter after the fire would be the same as the total mass of matter before the fire.

This burning campfire example illustrates a very important law in science: the law of conservation of mass. This law states that matter cannot be created or destroyed. Even when matter goes through a physical or chemical change, the total mass of matter always remains the same.