Question

Question #23d6b

Answer 1

No, mass is always conserved.

Explanation:

What is going on in the two examples is a chemical reaction.

With iron rusting, the mass increases due to oxygen bonding with the iron to form irion(III) oxide (`"Fe"_2"O"_3`), iron(II) oxide (`"FeO"`) or iron*II, III) oxide (`"Fe"_2"O"_3 * "FeO"`) depending on the situation and conditions:

`2"Fe"_ ((s))+"O"_ (2(g))->2"FeO"_((s))`

`4"Fe"_ ((s))+3"O"_ (2(g))->2"Fe"_ 2"O"_(3(s))`

`3"Fe"_ ((s))+3"O"_ (2(g))->"Fe"_ 2"O"_3*"FeO_ ((s))`

As you can see from each reaction, the iron has bonded with oxygen atoms, and therefore increase the mass of the iron nail with rust on it.

For the example with that match:
The mass stays constant as shown for the reactions based on the match head. However, the wood of the matchstick will also burn releasing gases like `"CO"_2` which float away from the matchstick,, leaving less mass behind.