Question

Iron is a solid, gray metal. Oxygen is a colorless gas. When they chemically combine, rust is made. Rust has a reddsh brown color. Why is rust different from the iron or oxygen that it is made of?

Answer 1

Because they react.

Explanation:

Iron(`Fe^(2 or 3)`) reacts with oxygen creating two oxides:
`2Fe^(+2) + O_2 -> 2FeO` If it is Iron(II), create Iron(II) oxide;
`2Fe^(+3) +3O_2 ->Fe_2O_3` If it is Iron(III), create Iron(III) oxide (or Ferric oxide).

The color before the reaction only matter if both reagents are liquid or aqueous and if they don't react.