Fusion Energy Released in Proton-Proton Chain
Use E=mc2 to do accounting
Mass is a measure of the energy stored in a system
Loss of mass from a system means release of energy from that system
Compare mass of four 1H to mass of one 4He
6.693 10-27 kg - 6.645 10-27 kg = 0.048 10-27 kg drop in mass
E = mc2 = 0.048 10-27 kg (3 108 m/s)2 = 0.43 10-11 kg m2/s2 = 0.43 10-11 J
(note == a Joule is just shorthand for kg m2/s2)
So 4.3 10-12 J of energy released
This is huge compared to chemical energy: 2.2 10-18 J to ionize hydrogen