9702 · 23.1
Mass defect and nuclear binding energy — FAQ
Frequently asked questions for 9702 Mass defect and nuclear binding energy. Direct answers first, then deeper explanation — then practise with marking.
Why is the mass of a nucleus always less than the sum of its individual protons and neutrons?
When protons and neutrons combine to form a nucleus, some of their mass is converted into energy to bind them together. This "missing" mass is called the mass defect, and the equivalent energy is the binding energy, which is released during the formation of the nucleus.
How does Einstein's E=mc² relate to mass defect and binding energy?
The formula E=mc² directly links the mass defect (Δm) to the nuclear binding energy (ΔE). It means that the energy released when a nucleus forms (or absorbed to break it apart) is precisely equivalent to the change in mass, multiplied by the square of the speed of light.
What is the most stable nucleus, and why is this important for nuclear reactions?
Iron-56 (Fe-56) is one of the most stable nuclei, as it has one of the highest binding energies per nucleon. This is important because nuclear reactions (fusion and fission) tend to move towards forming more stable nuclei. Lighter nuclei fuse to get closer to iron, and heavier nuclei fission to also get closer to iron, both processes releasing energy.