Nuclear Physics, Binding Energy

Overview

This lesson explains why nuclei can release energy even when nucleon number and charge are conserved. You will use nuclear equations, mass defect, binding energy, and binding energy per nucleon to compare fission and fusion reactions.

What You Need to Know

• Nuclear equations must conserve nucleon number and proton number.
• Mass and energy are equivalent, so a decrease in mass in a nuclear reaction corresponds to energy released.
• Mass defect is the difference between the separate nucleon masses and the mass of the bound nucleus.
• Binding energy is the energy needed to separate a nucleus completely into its nucleons.
• Binding energy per nucleon shows nuclear stability. Nuclei near iron are the most tightly bound.
• Fusion of light nuclei and fission of heavy nuclei can both release energy by moving products toward a higher binding energy per nucleon.

How to Work Through It

1. Balance nuclear equations by checking total nucleon number and total proton number.
2. Calculate mass defect from given nuclear or particle masses.
3. Convert mass defect to energy using E = mc^2, keeping units consistent.
4. Use a binding energy per nucleon graph to explain whether fusion or fission is energetically favourable.

Check Your Understanding

• What quantities must be conserved in a nuclear equation?
• Why is the mass of a bound nucleus less than the total mass of its separate nucleons?
• How does the binding energy per nucleon graph explain energy release in fusion and fission?
• Can you convert a small mass change into an energy release in joules?

Common Mistakes

• Treating mass defect as missing matter rather than mass-energy stored in the binding of the nucleus.
• Forgetting to convert atomic mass units or MeV into the requested unit.
• Using total binding energy when the question asks for binding energy per nucleon.
• Saying all fusion or all fission reactions release energy without linking the claim to the graph.

Next Steps

• Practise one full binding energy calculation with clear unit conversion.
• Carry the photon energy idea into the next lesson on the photoelectric effect.