# Why is FeCl3 the product, when Fe and Cl2 reacts and not FeCl2?

Apr 2, 2015

When iron is heated in a stream of dry chlorine the product is iron(III) chloride. This happens because chlorine is a powerful oxidising agent so brings out the higher oxidation state of iron:

$2 F {e}_{\left(s\right)} + 3 C {l}_{2 \left(g\right)} \rightarrow 2 F e C {l}_{3 \left(s\right)}$

To make iron(II) chloride you can react XS iron with dilute hydrochloric acid:

$F {e}_{\left(s\right)} + 2 H C {l}_{\left(a q\right)} \rightarrow F e C {l}_{2 \left(a q\right)} + {H}_{2 \left(g\right)}$

Apr 2, 2015

$F e C {l}_{3}$ is nearly twice as stable as $F e C {l}_{2}$ relative to the elements, $F e + C {l}_{2}$, so the system can dramatically lower the energy of the electrons in the system by rearranging in this way.

The extra stability of $F e C {l}_{3}$ can be explained by the fact that the central $F e$ atom is in the +3 formal oxidation state, and therefore has 5 electrons in its $3 d$ orbitals.

This is exactly half of the maximum number (10) that can be accommodated, so it represents a particularly stable situation.