Nuclear Reactions

1. Definitions (Must Know)

A. Nuclear reaction

A nuclear reaction involves a change in the nucleus (rearrangement of nucleons), producing new nuclides and/or particles.

B. Nuclear equation

A nuclear equation is a balanced equation written in nuclide notation, e.g.: ¹⁴₇N + ⁴₂He → ¹⁷₈O + ¹₁H

C. Conservation laws (nuclear processes)

In nuclear processes, you apply conservation of:

• nucleon number A
• charge (proton number) Z
• mass–energy
• momentum

2. Key Ideas (What Earns Marks)

• Balance nuclear equations by checking A and Z separately (both must match on left and right).
• If products have greater total mass than reactants, the reaction needs input kinetic energy (endothermic).
• If reactants have greater total mass than products, energy is released (exothermic): E_released = Δ m c²

3. Detailed Explanations

A. How balancing works

Example idea: if you know three of the four nuclides/particles, the missing one can be found by:

• subtracting nucleon numbers to match A,
• subtracting proton numbers to match Z.

B. Energy considerations

Define the mass defect for a reaction: Δ m = m_reactants-m_products

Then:

• if Δ m > 0, energy is released,
• if Δ m < 0, energy must be supplied.

4. Common Mistakes

• Balancing A but forgetting to balance Z.
• Treating γ emission as changing A or Z (it does not; γ is a photon).
• Using chemical symbols without nuclide notation when the question expects ^A_ZX.

5. Exam Tips

• State explicitly what is conserved: “nucleon number and charge are conserved”.
• Use a quick check: sum of top numbers left = sum of top numbers right; same for bottom numbers.
• If asked about energy: always link to E = Δ m c².

6. Worked Examples

7. Mind Stretchers