Nuclear fusion
4 marks · NormalNuclear reactions can involve either fission or fusion.
State one similarity and one difference between nuclear fission and nuclear fusion.
Explain why nuclear fusion requires much higher temperatures and pressures than fission.
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(a) Both fission and fusion are nuclear processes that release energy. In fission, a large nucleus splits into smaller ones; in fusion, small nuclei join to form a larger one.
(b) Fusion requires extremely high temperatures and pressures so that the positively charged nuclei have enough kinetic energy to overcome their electrostatic repulsion and collide.
Common mistakes: mixing up energy released per reaction; confusing requirement for slow vs fast neutrons
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Marking points
B1 (a) · 1 mark · One valid similarity, e.g. both release large amounts of energy.
B2 (a) · 1 mark · One valid difference, e.g. fission splits large nuclei, fusion joins small nuclei.
B3 (b) · 1 mark · States that high temperature/energy is needed to overcome repulsion between nuclei.
B4 (b) · 1 mark · Mentions role of pressure in increasing probability of collision (or similar).
Worked solution
a) Similarity: Both fission and fusion are nuclear reactions that release large amounts of energy. Difference: Fission splits a heavy nucleus into smaller nuclei; fusion combines light nuclei to form a heavier nucleus.
b) Fusion requires much higher temperatures and pressures because the nuclei involved are both positively charged and repel each other very strongly. High temperatures give the nuclei enough kinetic energy to overcome this repulsion, and high pressures increase the chance of the nuclei colliding and fusing.