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

2 Answers
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:

#2Fe_((s))+3Cl_(2(g))rarr2FeCl_(3(s))#

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

#Fe_((s))+2HCl_((aq))rarrFeCl_(2(aq))+H_(2(g))#

Apr 2, 2015

#FeCl_3# is nearly twice as stable as #FeCl_2# relative to the elements, #Fe+Cl_2#, so the system can dramatically lower the energy of the electrons in the system by rearranging in this way.

The extra stability of #FeCl_3# can be explained by the fact that the central #Fe# atom is in the +3 formal oxidation state, and therefore has 5 electrons in its #3d# orbitals.

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