# Why is the rusting of an iron pole not a physical change?

Both processes manifestly occur when iron metal oxidizes to give $F e O$ and $F {e}_{2} {O}_{3}$. We've all seen pictures of the monumental bridges around the world, the Golden Gate on the west coast of the States, the Hell's Gate bridge in New York, and of course the Sydney Harbour Bridge. To this day there would be dedicated teams of corrosion engineers assessing the extent of oxidation, and trying to control the process.