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Mass–energy in nuclear reactions
Intermediate
Small mass changes give large energy.
Reactions change rest masses; the difference Δm appears as kinetic energy. In fission of U-235 about 0.1% of the mass is released.
Δm = 0.2 u gives 200 MeV.
Energy per kg is millions of times chemical energy.
In more detail
In nuclear reactions, the small mass difference between reactants and products is released as energy, E = Δm c². This is the origin of nuclear power and the energy of stars.
Real-world uses
- Nuclear reactors release energy from the mass difference in fission.
- Stars shine because fusion converts mass into energy.
- Nuclear engineers compare the mass lost in fission with the energy released to estimate reactor output.
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Frequently asked questions
How much mass is lost in fission?
About 0.1 percent of the mass of the fissioning nuclei.
Is mass really lost?
The mass of the products is less, and the difference appears as kinetic and radiant energy.
How small is the mass change?
It is tiny compared with the total mass, but multiplied by c squared it gives an enormous amount of energy.
Related topics in Relativity
Four-vectors · Relativistic collisions · Particle accelerators and relativity · Relativistic electromagnetism · Tachyons · Equivalence principle