IB MYP 4-5 Chemistry -Nuclear Fission and Fusion- Study Notes - New Syllabus
IB MYP 4-5 Chemistry -Nuclear Fission and Fusion- Study Notes
Key Concepts
- Nuclear Fission and Fusion
Nuclear Fission and Fusion
Nuclear Fission and Fusion
Nuclear fission and nuclear fusion are two different types of nuclear reactions that release enormous amounts of energy from atomic nuclei.
- Fission: The splitting of a heavy nucleus into two smaller nuclei.
- Fusion: The joining of two light nuclei to form a heavier nucleus.
Nuclear Fission
Nuclear fission is the process in which a heavy atomic nucleus, such as uranium-235 or plutonium-239, splits into two lighter nuclei when bombarded by a neutron, releasing a large amount of energy and more neutrons.
Example (Uranium-235 fission reaction):
\( \mathrm{^{235}_{92}U + ^1_0n \rightarrow ^{141}_{56}Ba + ^{92}_{36}Kr + 3^1_0n + \text{Energy}} \)
- Each fission releases about 200 MeV of energy.
- The emitted neutrons can cause further fissions, leading to a chain reaction.
Chain Reaction:
- Occurs when released neutrons from one fission event trigger more fissions.
- Controlled chain reactions occur in nuclear reactors (for power generation).
- Uncontrolled chain reactions occur in atomic bombs.
Control of Fission in Reactors:
- Moderator: Slows down fast neutrons (e.g., water or graphite).
- Control rods: Absorb excess neutrons (made of cadmium or boron).
- Coolant: Removes heat from the reactor core.
Nuclear Fusion
Nuclear fusion is the process in which two light atomic nuclei combine to form a heavier nucleus, releasing even more energy than fission.
Example (Hydrogen fusion in the Sun):
\( \mathrm{^2_1H + ^3_1H \rightarrow ^4_2He + ^1_0n + \text{Energy}} \)
- Occurs at extremely high temperatures (≈ 10⁷ K) and pressures, as in the Sun.
- Fusion of hydrogen isotopes (deuterium and tritium) produces helium and energy.
- Fusion releases about 3–4 times more energy than fission per unit mass.
Equation (Simplified solar fusion process):
\( \mathrm{4 ^1_1H \rightarrow ^4_2He + 2^0_{+1}e + 2\nu + \text{Energy}} \)
Key Idea: Fusion is the source of the Sun’s energy and represents the ultimate clean energy source for the future — if controlled safely on Earth.
Comparison of Nuclear Fission and Fusion
| Aspect | Nuclear Fission | Nuclear Fusion |
|---|---|---|
| Definition | Splitting of a heavy nucleus into two lighter nuclei. | Joining of two light nuclei into a heavier nucleus. |
| Typical Reactants | \( \mathrm{U^{235},\ Pu^{239}} \) | \( \mathrm{H^2,\ H^3} \) (Deuterium, Tritium) |
| Energy Released | ~200 MeV per reaction | ~300–400 MeV per reaction |
| Conditions Required | Can occur at room conditions (in reactors). | Requires very high temperature and pressure. |
| Products | Two smaller nuclei, 2–3 neutrons, energy. | Helium nucleus, neutron, energy. |
| Radioactive Waste | Produces long-lived radioactive waste. | Very little or no radioactive waste. |
| Examples | Nuclear power plants, atomic bombs. | Sun, hydrogen bombs, experimental reactors. |
Applications
- Fission: Used in nuclear power plants to produce electricity and in atomic weapons.
- Fusion: Provides energy in stars; being developed for future clean power (e.g., ITER project).
Equation (Nuclear Reactor Example):
\( \mathrm{^{235}_{92}U + ^1_0n \rightarrow ^{141}_{56}Ba + ^{92}_{36}Kr + 3^1_0n + \text{Energy}} \)
Safety and Environmental Concerns
- Fission reactors produce radioactive waste requiring safe storage for thousands of years.
- Fusion, if controlled, produces minimal waste and is safer — but requires extremely high energy to start.
- Both processes must be carefully managed to prevent radiation leaks or accidents (e.g., Chernobyl, Fukushima).
Summary Table: Fission vs Fusion Overview
| Reaction Type | Description | Energy Efficiency |
|---|---|---|
| Fission | Splitting of heavy nuclei, controlled in reactors. | High, but produces waste. |
| Fusion | Combining light nuclei, occurs naturally in stars. | Very high, clean, but hard to control. |
Example
Write the nuclear equation for the fission of uranium-235 when bombarded by a neutron.
▶️ Answer / Explanation
Step 1: Uranium-235 absorbs a neutron and becomes unstable.
Step 2: \( \mathrm{^{235}_{92}U + ^1_0n \rightarrow ^{141}_{56}Ba + ^{92}_{36}Kr + 3^1_0n + \text{Energy}} \)
Final Answer: The fission releases 3 neutrons and a large amount of energy.
Example
Explain why fusion reactions are difficult to carry out on Earth.
▶️ Answer / Explanation
Step 1: Fusion requires very high temperatures (millions of °C) and pressures.
Step 2: At such conditions, positively charged nuclei can overcome electrostatic repulsion.
Step 3: These conditions are hard to achieve and maintain safely on Earth.
Final Answer: Fusion is difficult on Earth because the nuclei must collide with enough energy to overcome strong repulsive forces.
Example
Compare the advantages and disadvantages of using nuclear fission and fusion as energy sources.
▶️ Answer / Explanation
Step 1: Fission provides large energy and is currently usable but produces radioactive waste.
Step 2: Fusion provides even greater energy with no long-lived waste but requires extreme conditions.
Step 3: Fusion is safer and more sustainable if technology can control it.
Final Answer: Fission is practical but polluting; fusion is clean and powerful but technologically challenging.