What happens when water vapour is passed over red hot iron?

When water vapour (steam) is passed over red-hot iron, a chemical reaction occurs where the iron displaces hydrogen from the water. This process results in the formation of magnetic iron oxide, also known as magnetite (Fe3O4), and hydrogen gas [t1][t2]. The balanced chemical equation for this reversible reaction is 3Fe + 4H2O (steam) → Fe3O4 + 4H2 [t3][t7]. While iron does not react with cold or hot liquid water, it reacts specifically with steam at high temperatures [c3][t4]. Magnetite (Fe3O4) is a mixed oxide containing both iron(II) and iron(III) states, often referred to as ferrous-ferric oxide [t9]. Although some sources might incorrectly suggest Fe2O3, standard chemical principles and the majority of scientific evidence confirm that the primary solid product in this specific high-temperature reaction with steam is Fe3O4 [t2][t7].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > Activity 3.10 > p. 43