Rust — Iron Oxidation
Iron slowly burning
Rusting is an oxidation reaction. Chemically, it's essentially the same reaction as combustion (fire). The only difference is speed.
The Reaction
4Fe + 3O₂ + 6H₂O → 4Fe(OH)₃ → 2Fe₂O₃·3H₂O
Iron (Fe) reacts with oxygen (O₂) in the presence of water (H₂O), forming iron hydroxide then iron oxide (rust).
Why Water Is Needed
Pure oxygen alone doesn't rust iron easily. Water acts as a medium for electron transfer. That's why iron structures near the coast rust faster — saltwater is an electrolyte that facilitates electron transfer.
Hand Warmers
Open a disposable hand warmer and you'll find iron powder inside. Shaking the packet exposes iron powder to air, triggering rapid oxidation. The heat from this reaction warms your hands.
A perfect everyday example of rusting generating heat.
Rust Prevention
Paint/coating: Physically blocks oxygen and water from reaching iron. The most basic method.
Galvanizing (zinc plating): Zinc oxidizes before iron does. Sacrificial anode approach.
Stainless steel: Adding chromium creates a protective chromium oxide layer on the surface.
How It Works
Iron loses electrons when exposed to water and oxygen (oxidation)
Water acts as electrolyte → electrons transfer, forming iron hydroxide
Iron hydroxide dehydrates → iron oxide (Fe₂O₃) = brown rust complete