What is the chemical formula for rust?

The exposure of iron or an alloy of iron to oxygen in the presence of moisture prompts the formation of rust. This response isn't prompt, it generally continues over a considerably large time period. The oxygen molecules bond with iron atoms, bringing about the formation of iron oxides. This weakens the bonds between the iron atoms in the structure. The response of the rusting of iron includes an expansion in the oxidation condition of iron, joined by lost electrons. Rust is mostly made up of two different oxides of iron that differ in the oxidation condition of the iron particle. These two oxides are

1. Iron(II) oxide or ferrous oxide. The oxidation state of iron in this compound is +2 and its chemical formula is FeO. 
2. Iron(III) oxide or ferric oxide, where the iron atom exhibits an oxidation state of +3. The chemical formula of this compound is Fe2O3.

The rusting of iron is an electrochemical procedure that starts with the exchange of electrons from iron to oxygen. The iron is the reducing agent (gives up electrons) while the oxygen is the oxidizing agent (gains electrons). The rate of corrosion is influenced by water and quickened by electrolytes, as illustrated by the impacts of road salt on the corrosion of automobiles. The key reaction in the decrease of oxygen is formulated as

O2 + 4  e− + 2  H2O → 4  OH−

Since it forms hydroxide particles, this procedure is strongly affected by the presence of corrosive(acid). The corrosion of most metals by oxygen is quickened at low pH. Giving the electrons to the above response is the oxidation of iron that might be described as follows:

Fe → Fe2+ + 2  e−

The following redox response likewise happens in the presence of water and is necessary to the formation of rust:

4 Fe2++ O2 → 4 Fe3+ + 2 O2−

In addition, the following multistep acid-base reactions influence the course of rust formation:

Fe2+ + 2  H2O ⇌ Fe(OH)2 + 2  H+

Fe3+ + 3  H2O ⇌ Fe(OH)3 + 3  H+

As do the following dehydration equilibria:

Fe(OH)2 ⇌ FeO + H2O

Fe(OH)3 ⇌ FeO(OH) + H2O

2 FeO(OH) ⇌ Fe2O3 + H2O

From the above conditions, it is additionally observed that the corrosion products are directed by the accessibility of water and oxygen. With limited dissolved oxygen, iron(II)-containing materials are favored, including FeO and dark lodestone or magnetite (Fe3O4). High oxygen concentrations support ferric materials with the nominal formulae Fe(OH)3−xO​x⁄2. The idea of rust changes with time, reflecting the slow rates of the responses of solids.

Rusting is a kind of Chemical Change. It brings about the arrangement of Iron Oxide which is a totally new substance. The rustless materials which are used for construction are available at our steeloncall.com. Final Chemical Reaction of Rusting is as per the following:

Iron + Oxygen (from the environment) + Water (Humidity) —> Iron Oxide (Rust)

Fe + O2 + H2O —> FeO and Fe2O3