I was told the mass defect of an atom is the difference in mass of the atom versus it's particles, for example:

carbon 12 is less massive than 6 protons + 6 neutrons + 6 electrons.

this negative difference means carbon has a negative mass defect, thus energy is released when carbon is formed, or energy is required to split carbon into it's particles.

more mass -> less mass + energy

right?

so...

for deuterium + deuterium -> either (neutron + He-3) or (proton + tritium), I would assume that a less massive product would also yield more energy. In these reactions, the reactants are the same, but I'm reading that the He-3 reaction generates 3.27 MeV and the tritium reaction generates 4.03 MeV. http://hyperphysics.phy-astr.gsu.edu/hbase/NucEne/fusion.html. is this value per nucleon or something?

>picrel

Since the tritium reaction yields more energy, how can it be that tritium is heavier (more massive) than He-3?

Tritium: 3.0160492 u
He-3: 3.0160293 u

If tritium has more mass than He-3, shouldn't that reaction produce less energy?

Is the extra proton and neutron in each reaction weighed differently?