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7.4.1Acids, Bases and Salts

Nuclear Fusion — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions

5 min read 5 parts Lesson 11 of 11 Unit quiz

📚 Cambridge IGCSE Chemistry 0620 Hub / Topical Revision
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Curriculum Equation Key Radioactive Decay & Half-Life FormulasFast Exam Solution
N(t) = N₀ × (1/2)t / t½ | λ = ln(2) / t½ ≈ 0.693 / t½ | E = Δm × c²
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Part 1 of 5What Fusion Is

7.4.1 Nuclear Fusion
Fusion
  • Two light nuclei join to form a heavier nucleus, releasing a large amount of energy from the nuclear store.
Stars
  • Stars such as the Sun fuse hydrogen nuclei into helium nuclei, and this fusion provides their energy output.
Equation example
  • Deuterium and tritium fuse to form helium-4 and a neutron: ²₁H + ³₁H → ⁴₂He + ¹₀n, with both sides balanced.
Mass loss
  • The product has slightly less mass than the reactants, and this lost mass is converted into energy.

Part 2 of 5Conditions for Fusion

1
Nuclei are positively charged, so they repel one another as they approach.
2
To overcome this repulsion, the nuclei need very high kinetic energy, which requires a very high temperature.
3
High pressure increases the density of particles, which makes collisions with enough energy more likely.
4
Very high temperature and pressure are therefore needed together, which is why fusion is hard to achieve on Earth.

Part 3 of 5Fusion on Earth

Fusion on Earth
Containment
  • Holding the very hot fuel in place is very difficult, so only a small amount of fusion can be achieved at present.
Energy balance
  • Creating the temperatures needed requires a great deal of energy, so a net gain has not yet been achieved.
Fuel
  • Hydrogen isotopes are plentiful, and fusion releases very large amounts of energy for each kilogram of fuel.
Stars
  • Stars use their own gravity to create the high pressure in their cores, which is not possible in Earth-based devices.

Part 4 of 5Worked Example

Question

  • A fusion reaction releases 6.0 × 10¹² J of energy.
  • Calculate the mass lost.
  • The speed of light is 3.0 × 10⁸ m/s.

  1. Rearrange E = mc² to give m = E ÷ c².
  2. c² = (3.0 × 10⁸)² = 9.0 × 10¹⁶ m²/s².
  3. m = 6.0 × 10¹² ÷ 9.0 × 10¹⁶ = 6.7 × 10⁻⁵ kg.

Answer 6.7 × 10⁻⁵ kg

Part 5 of 5Exam Checklist & Tips

7.4.1 – Key Points for the Exam

  • Nuclear fusion The joining of two light nuclei to form a heavier nucleus, releasing energy.
  • Mass-energy equivalence The relationship E = mc² between a loss of mass and the energy released.
  • Loss of mass The difference between the mass of the reactants and the products in a nuclear reaction.
  • Repulsion The force that pushes two positively charged nuclei apart.
  • Deuterium An isotope of hydrogen with one proton and one neutron in its nucleus.

Common Mistakes

  • Forgetting to square the speed of light in E = mc², which gives an incorrect energy value.
  • Describing fusion as the splitting of nuclei; fission splits nuclei and fusion joins them.
  • Using a mass in grams in E = mc²; the mass must be in kilograms so that the energy is in joules.
  • Saying the energy comes from chemical bonds; it comes from the nuclear store and the loss of mass.

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