What happens if too much is given during a transmutation? 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 &quot;giving too much&quot; here. @Becuzz's answer touches on this, but I want to expand on it as well as talk about the human transmutation.
Giving &quot;too much&quot;
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 &quot;amounts&quot; 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 &quot;too much&quot; 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.
Human transmutation

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.
Related reading

When Edward and Alphonse try to transmute their mother, how come they didn&#39;t gain anything?
If the &quot;Truth&quot; didn&#39;t exist, would that mean that feats such as Human Transmutation would work?