When iron rusts, iron metal (Fe) reacts with oxygen molecules (O2) to form iron rust (Fe2O3).

Question

Why is this change a chemical reaction?

Responses

Iron and oxygen atoms rearrange themselves to form iron rust. Iron rust did not exist before the reaction.
Iron and oxygen atoms rearrange themselves to form iron rust. Iron rust did not exist before the reaction.

Oxygen atoms are very reactive. Any change that involves oxygen is a chemical reaction.
Oxygen atoms are very reactive. Any change that involves oxygen is a chemical reaction.

There are two substances involved in this change. When two substances are involved in a change, it is a chemical reaction.
There are two substances involved in this change. When two substances are involved in a change, it is a chemical reaction.

Oxygen is a gas, and iron rust is a solid. Any change that turns a gas into a solid is a chemical reaction.

Answer 1

The best response to explain why the rusting of iron is a chemical reaction is:

Iron and oxygen atoms rearrange themselves to form iron rust. Iron rust did not exist before the reaction.

This response correctly identifies that during the rusting process, the atoms of iron and oxygen undergo a chemical change, resulting in the formation of a new substance (iron rust, Fe2O3) that did not exist prior to the reaction. Chemical reactions involve the breaking and forming of bonds between atoms, which leads to the creation of new substances.