In Brotherhood, during a transmutation, what happens if too much is given as a part of the equivalent exchange? In the series, the brothers lose something each for trying to give too little during the human transmutation attempt to bring back their mom... So what would happen if they give too much? Anything at all?
There is no such thing as "giving too much" here. @Becuzz's answer touches on this, but I want to expand on it as well as talk about the human transmutation.
Giving "too much"
Alchemy (in the FMA canon) is basically chemistry. I will assume anyone reading this has not taken much (or any) chemistry in their life, so I'll try to keep it relatively simple.
Imagine you have a lighter filled with benzene. When you light it, and it starts burning, a chemical reaction is taking place, transforming benzene (C6H6) and oxygen (O2), into carbon dioxide (CO2) and water (H2O). You can represent this as an equation showing the "amounts" of each compound required.
What happens if you put in 25 of O2 instead of 15? Simple: the 10 remaining O2 will not be used.
Transmutation, while more complex scientifically, obeys the same principle. If we're transmuting a block of lead into gold, we will get an equivalent amount of gold as the lead that we transmuted. Giving "too much" lead will result in either excess gold (if there is enough transmutation energy), or leftover lead (if it is not transmuted). The amount of gold will always be chemically equivalent to the amount of lead consumed in the reaction.
TL;DR: The chemical amount consumed in the reaction will always equal the chemical amount of the product created.
In the series, the brothers lose something each for trying to give too little during the human transmutation attempt to bring back their mom
This isn't exactly correct. I get what you're trying to say, but it's not quite accurate.
The brothers gave exactly what they needed to get their mother back, right down to the soul data from their own blood. The reason they didn't succeed is because they could not provide her human life to go inside the body they created (which was actually a pretty good attempt for pre-teen prodigy knowledge of human anatomy). Add to that, of course, that God does not permit resurrection of this human life, and you've got a recipe for disaster.
The reason they lose their bodies proper is because they had to pay a toll to go inside the Gate (yes, against their will, as punishment). In the eyes of the beings overseeing this transmutation, the exchange was equivalent:
- The materials (carbon, water, etc.) given were consumed and created the blackened beast.
- Edward lost his leg and saw some knowledge within the Gate.
- Alphonse lost his body and saw a lot of knowledge within the Gate.
- Edward lost his arm and brought back Alphonse's soul from beyond the Gate.
In the end, neither too much nor too little was given, and the transmutation obeyed equivalent exchange.
I don't believe that you even can pay too much. The law of equivalent exchange would dictate that if you put in a quantity X of dirt and transmuted it to gold, you should get the exact equivalent amount of gold out, no less.
In terms of paying more (as Ed and Al did) there is a fairly good explanation in episode 26 "Reunion". (Spoilers ahead)
Ed, Ling and Envy are inside of Gluttony. Ed explains that a failed transmutation (which I assume would include paying too much, if such a thing is even possible) "ricochets back onto the one that performed it", whatever that means. To me it sounds like it just doesn't work. Though in this case it sounds like less of "paying to much" and more of "trying to do something that just plain doesn't work."
Ed also gives a very good explanation of what human transmutation really is in that same episode. He states that human transmutation (as they wanted to do to bring back their mom) just isn't a thing. Human transmutation really involves transmuting live humans, not bringing back the dead.
Later in the same episode, Envy explains that to open the Portal (which is really what Ed and Al did, they didn't actually transmute a human), they have to pay a toll. In the case of Ed and Al they paid with their bodies/body parts. In exchange the got to open the Portal and received the knowledge and power that came with it.