Energy Transformation in Chemical and Nuclear Reactions

Key Concepts

• Energy is transformed in chemical reactions.

• Energy is transformed in nuclear reactions.

• Energy is transformed when light energy interacts with matter.

Concept 2: Energy Transformation in Nuclear Reactions

• Radiation: A mechanism of energy transfer where atoms or molecules emit energy in the form of electromagnetic waves.

• Nuclear Decay: The change to an atom due to the emission of particles or radiation.

• Nuclear reactions involve changes to atomic nuclei, resulting in transformation into different elements and release of energy.

Types of Nuclear Reactions

• In chemical reactions, atoms are rearranged but not transformed. In nuclear reactions, atoms change from one element to another, often involving isotopes.

Isotopes

• Isotopes: Forms of the same element with an equal number of protons but a different number of neutrons.

• Radioactive Isotopes: Unstable isotopes that emit particles to become stable by shedding extra energy, often through radiation.

Alpha Decay

• Alpha Decay: A process where a nucleus emits an alpha (\alpha) particle (helium nucleus).

  • This results in a reduction of 2 protons and 2 neutrons in the nuclear structure, decreasing the mass number by 4 and atomic number by 2.

  • Example of Alpha Decay: Radium-226 decays to Radon-222:
    

    {^{226}{88}Ra \rightarrow ^{222}{86}Rn + ^{4}_{2}He + \text{energy}}

Beta Decay

• Beta Decay: A process where a neutron in the nucleus converts into a proton and emits a beta particle (electron).

  • The resultant nucleus has one less neutron and one more proton.

  • Example of Beta Decay: Lithium-8 decays to Beryllium-8:
    

    {^{8}{3}Li \rightarrow ^{8}{4}Be + \beta + \text{energy}}

Gamma Decay

• Following alpha or beta decay, some nuclei are left in an excited state and may emit a gamma (\gamma) ray to become stable.

  • Example of Gamma Decay involving Thorium-234:
    

    {^{234}{90}Th^{*} \rightarrow ^{234}{90}Th + \gamma}

Nuclear Fission

• Nuclear Fission: A process in which a heavier nucleus splits into lighter nuclei with energy release.

  • Occurs when a uranium-235 nucleus absorbs a neutron, resulting in fission and producing lighter elements and further neutrons.

  • Example Reaction:
    

    {^{235}{92}U + n \rightarrow ^{141}{56}Ba + ^{92}_{36}Kr + 3n + \text{energy}}

Fission Chain Reactions

• Chain Reaction: A process where one reaction prompts subsequent reactions.

  • In this context, the neutrons released can interact with other uranium-235 nuclei leading to further fissions and subsequently, much larger energy outputs.

Nuclear Reactors

• Nuclear reactors convert the thermal energy from fission reactions into electrical energy, predominantly utilizing uranium.

• Nuclear reactors require uranium-235 and manage fission reactions, employing coolant systems to transfer heat and produce steam for turbines.

Nuclear Fusion

• Nuclear Fusion: The process where two small nuclei combine to form a larger nucleus, requiring extremely high temperatures and pressure to overcome repulsion between protons.

• Common in stars, including the Sun, where isotopes deuterium ^{2}H and tritium ^{3}H fuse to yield helium-4 (^{4}He) and energy.

  • Reaction:
    

    {^{2}{1}H + ^{3}{1}H \rightarrow ^{5}{2}He \rightarrow ^{4}{2}He + n + \text{energy}}

• Benefits of fusion:

  • The energy released per unit mass from fusion reactions is significantly greater than that of fission.

  • The products of fusion are typically non-radioactive, leading to no nuclear waste.

Summary and Reflection Questions

1. Compare chemical reactions and nuclear reactions in terms of energy transformation.

2. Definition and characteristics of a radioactive isotope and its energy dissipation methods.

3. Distinctions between alpha decay and beta decay.

4. Reasons behind gamma decay occurrence.

5. Similarities and differences between nuclear fission and fusion.

6. Explanation of nuclear reactions adhering to the law of conservation of energy.