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