Explain why the energy released per kilogram of fuel in a nuclear fission reaction is many millions of times greater than the energy released per kilogram of fuel in a typical chemical combustion reaction.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Chemical reactions rearrange electrons and form or break chemical bonds, so the energy change is limited to the electromagnetic force.
Nuclear fission splits a heavy nucleus, changing the arrangement of protons and neutrons.
The strong nuclear force that binds nucleons is far stronger than the electromagnetic force that binds electrons, so each nucleon carries much more energy.
During fission a small mass defect is converted to energy via E=mc²; because c² is huge, even a tiny mass loss gives enormous energy per kilogram.
Nuclear fission splits a heavy nucleus, changing the arrangement of protons and neutrons.
The strong nuclear force that binds nucleons is far stronger than the electromagnetic force that binds electrons, so each nucleon carries much more energy.
During fission a small mass defect is converted to energy via E=mc²; because c² is huge, even a tiny mass loss gives enormous energy per kilogram.
Examiner tips
- Mention electron rearrangement vs nucleon rearrangement
- State strong force vs electromagnetic force
- Use E=mc² and mass defect
- Keep answer concise and use exact terminology
Common mistakes
- Confusing chemical bond energy with nuclear binding energy
- Ignoring the mass defect and E=mc²
- Using incorrect units or not specifying per kilogram
Mark scheme (4 marks)
- Chemical reactions involve rearrangement of electrons / breaking and forming of chemical bonds between atoms
- Nuclear fission involves changes within the nucleus itself, specifically the splitting of a heavy nucleus
- The nuclear force (strong force) binding nucleons together is far stronger than the electromagnetic force binding electrons to atoms, so much more energy is stored per particle in nuclear bonds
- In fission, a small amount of mass is converted directly into energy via E = mc²; because c² is very large, even a tiny mass defect yields enormous energy
Key terms in this question
Related
- All IB DP Physics Standard Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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