Do you mind explaining it to me? I still don't understand it lol
Sure, but since Im still trying to learn the concept, so please excuse me if I make any mistakes or get you confused:
I think the first thing that makes both of us make mistakes in this question is because we assume that, ALL redox reaction equations can be derived by adding water, H+ and stuff to both side without knowing when and where can we apply this concept.
Firstly, it is good to have a general idea of what is happening in a thermite process, the Fe2O3 and Al reacts together and generates extreme heat, this process is a redox reaction.
Before looking into the question, I guess you can write an overall equation for this:
Fe2O3 + Al -> Al203 + Fe (sorry I'm really lazy to include states)
You can see that: Fe goes from +3 to 0 and Al goes from 0 to +3. Hence, Fe undergoes reduction and Al undergoes oxidation. Oxygen is actually just a spectator ions, do not even involve much in the redox process.
In Fe2O3, you know that you have 2Fe(3+) and 3O (-2), hence, the decomposition reaction comes as:
Fe2O3 -> 2Fe + 3O(-2) If you question why at this stage, "2Fe" in the product has a charge of 0 but not +3, is because Fe has already gained 3 electrons from Aluminium, hence, it has successfully changed its charge to 0.
But we won't stop at that, since the equation is not balancing between the LHS and the RHS, since 3O (2-) carries a charge of -6, we need to add 6e- to the LHS as well. ( We are not adding H+ to balance because in this reaction, there's no way water can present, we are talking about solid substances producing extreme heat). So our final answer should be:
Fe2O3 + 6e -> 2Fe + 3O(-2)
I know my explanation is not good enough and might still contain some errors, but it's my best, hope this helps!