What is nuclear fission? Write a balanced equation for the fission of ²³⁵U, and explain with the binding energy curve why energy is released.

1. 1 · Define fission. A heavy nucleus absorbs a slow neutron and splits into two medium-mass nuclei, releasing energy and neutrons.
2. 2 · Write a balanced equation. ¹₀n + ²³⁵₉₂U → ¹⁴⁴₅₆Ba + ⁸⁹₃₆Kr + 3¹₀n + about 200 MeV (236 = 236; 92 = 92).
3. 3 · Explain the energy release. Ebn rises from about 7.6 MeV to about 8.5 MeV; about 0.9 MeV × 236 ≈ 200 MeV is released.
4. 4 · Say where the energy goes. It first appears as kinetic energy of the fragments and neutrons, and finally as heat in the surrounding matter.
5. 5 · Real life. Tarapur and Kudankulam use controlled fission to make electricity.
6. 6 · Close in one line. So, fission releases energy because the products are more tightly bound than the parent.

Scoring tip: Show the mass-number and atomic-number check under your equation. Examiners give a mark for a balanced equation.