Explain mass defect, E = Δmc² and the atomic mass unit.

Solution & explanation

Released energy corresponds to reactant rest mass exceeding product rest mass: Δm = mi − mf. E = Δmc² requires kilograms for joules. One u is one twelfth the mass of a neutral carbon-12 atom and is about 1.66054×10⁻²⁷ kg; 1 u c² ≈ 931.5 MeV. Use mass difference, not the full fuel mass, in ordinary nuclear reactions.