Question

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

Answer 1

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))`

Answer 2

`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.