# How is the reaction between hydrogen sulfide and iron chloride possible?

May 3, 2017

The reason has nothing to do with electronegativity.

#### Explanation:

Electronegativity is a measure of the attraction a neutral atom has for the shared electrons in a covalent bond

The reason has more to do with the relative energies of the two iron ions.

$\text{Fe"^"2+""(g)" → "Fe"^"3+" "(g)" + "e"^"-" ; I_3 ≈ "3000 kJ/mol}$

The third ionization energy of $\text{Fe}$ is quite high, so $\text{Fe"^"3+}$ is much less stable than $\text{Fe"^"2+}$.

In aqueous solution, $\text{Fe"^"3+}$ is slightly more stabilized by hydration than $\text{Fe"^"2}$, but that does not compensate for the high 3rd ionization energy.

In short, $\text{Fe"^"3+}$ is less stable than $\text{Fe"^"2+}$ and would like having another electron to reduce the charge.

Thus, $\text{Fe"^"3+}$ is quite capable of removing an electron from $\text{H"_2"S}$,