WHY IS fecl2 formed instead of fecl3 when iron reacts with dilute hydrochloric acid?

Answer 1

The free energy is such that the reaction is spontaneous for iron to be oxidized to iron(II) with HCl but not to iron(III). In fact, if any iron(III) were formed the thermodynamics are such that it would be reduced to iron(II) immediately with the excess iron therre initially. Iron(II) solutions must be protected from the atmosphere or oxygen will oxidize iron(II) to iron(III). Usually that is done by adding a small piece of iron metal to the iron(II) solution. So when oxygen oxidizes a ferrous ion to ferric ion the iron metal reacts with it to be oxidized to ferrous and the ferric is reduce to ferrous and the integrity of the ferrous solution is not compromised. I used to tell my students to observe the ferrous solution and see that small piece of iron in the bottom. That always made a good test question, "Why is the piece of iron metal in ferrous solution?"