# When Iron reacts with any other species, how will we know that the reaction will be of Fe(II) or Fe(III) i.e. of ferrous or ferric? [closed]

Like when iron reacts with water there forms iron oxide and hydrogen but how'll we come to know which of three equation will be right equation for reaction?

$$\ce{Fe + H2O → FeO + H2}$$

$$\ce{2Fe + 3H2O → Fe2O3 + 3H2}$$

$$\ce{3Fe + 4H2O → Fe3O4 + 4H2}$$

• There are no general rules ! Of course the oxidation of iron passes always by the level Fe(II). But sometimes the oxidation goes immediately to the the level Fe(III). It depends on the nature of the oxidant. If $\ce{Fe}$ reacts with $\ce{HCl}$ it produced $\ce{FeCl2}$, as the $\ce{H2}$ produced would be able de reduce $\ce{FeCl3}$ to $\ce{FeCl2}$. If $\ce{Fe}$ reacts with $\ce{Cl2}$, it produces $\ce{FeCl3}$, as $\ce{Cl2}$ is able to oxidize $\ce{FeCl2}$ to $\ce{FeCl3}$ – Maurice Dec 17 '20 at 10:47
• Note that there is an almost general rule, that oxides of metals with multiple (and close) oxidation states, like Fe, Mn, Co, Ni form frequently non-stoichiometric oxides, where atomic ratios are not a ratio of small integers. E.g. iron(II) oxide with theoretical composion FeO has the real composition Fe(0.84)O to Fe(0.95)O. – Poutnik Dec 17 '20 at 11:41
• It depends, in many cases, on how much of the reactant is present to force the reaction to a higher oxidation state. See en.wikipedia.org/wiki/Law_of_mass_action – DrMoishe Pippik Dec 18 '20 at 3:05

$$\ce{Fe^3+}$$ is the stable form of iron in atmospheric oxygen partial pressures, this in such conditions $$\ce{Fe2O3}$$ (hematite) will always be the stable product. The lower oxidation state oxides (such as magnetite $$\ce{Fe3O4}$$ and wüstite ~$$\ce{FeO}$$) can only stably form in deep earth environments, or in special controlled atmosphere reaction chambers.