Redox reaction of iron III oxide and carbon monoxide

Question

Balancing redox reaction by Oxidation number method:

Fe2O3 + CO ➡️ Fe(s) + CO2

in this oxidation reduction reaction the iron goes from a +3 charge to zero while the carbon goes from +2 to +4. Because of the unbalanced number of electrons,

you would need to times each half reaction by the common multiple.

2 (Fe2O3 ➡️ Fe )

3 ( CO ➡️ CO2)

after this the final equation will be

Fe2O3 + 3CO ➡️ 2Fe + 3CO2

My question is why would you not put a 2 in front of Fe2O3

Like you would in other redox reactions examples such as :

2H2 + O2 ➡️ 2H20

So I’m confused when you need to put an integer in front of a compound or element when multiplying the half reactions by common multiple. Hope that makes sense! Thanks!

Answer 1

The half reaction involving Fe is

Fe₂O₃ + 6H⁺ + 6e-—> 2Fe + 3H2O (eq 1)

The half reaction involving C is

CO + H2O—> CO₂ + 2H⁺ + 2e- (eq 2)

multiply eq 2 by 3 to equalize electrons and add the two equations to end up with

Fe₂O₃ + 3CO —> 2Fe + 3CO₂

This is the way you should balance such a redox reaction.

Answer 2

You wouldn't. Think of the Fe as going from Fe₂ → 2 Fe and it will make better sense.