Nuclear Reactions & Energy Nuclear fission and fusion are processes that involve extremely large amounts of energy. Fission = the splitting of a large nucleus into two smaller nuclei, subatomic particles and energy Fusion = the joining of nuclei See page 312
Fission Large nuclei tend to be unstable due to repulsive forces between protons To increase stability atoms may split into different atoms with lighter nuclei This is accompanied by a large release of energy Can be used to generate power However nuclear reactors produce radioactive waste As well nuclear weapons are a concern
Review of Chemical Reactions Law of conservation of mass A + B AB, the mass of the reactants is equal to the mass of the reactants # of protons=atomic #= atoms identity Chemical reactions =change in electron arrangement Change in energy is relatively low
Nuclear Reactions Reactions involving a change in an atoms nucleus Process in which an atoms nucleus changes by gaining or releasing particles/energy Can be 1, 2 or all 3 types of subatomic particles (protons, neutrons, electrons) as well as gamma rays. In a nuclear reaction the small change in mass results in a large change in energy Ex- Nuclear fission of 1 gram of pure Uranium-235 Releases the same amount of energy as burning 2 tonnes of coal.
Nuclear Equations for Induced Nuclear Reactions Natural radioactive decay consists of the release of alpha, beta and gamma radiation. It is possible to force a nucleus to become unstable Nuclear reaction occurs immediately Can be induced by bombarding a nucleus with alpha particles, beta particles or gamma rays This reaction is similar to other types of decay, but the difference is that the particles are part of the REACTANTS. N-14 bombarded by alpha particle, turns into f-18 which quickly decays into O-17 and a proton. 4 2 + 14 7 N 17 8 O + 1 1 p or 4 2He + 14 7 N 17 8 O + 1 1 H See pages 314-315
The rules for writing these equations are the same as earlier nuclear equations 1. Mass numbers must equal on both sides of the equation 2. Charges (represented by atomic # s) must equal on both sides of the equation Sub atomic Particle symbols
Nuclear Fission Nuclear energy used to produce power or nuclear weapons comes from nuclear fission. Nuclear fission is the splitting of one heavy nucleus into two or more smaller nuclei, some sub-atomic particles, and energy. A heavy nucleus is usually unstable, due to many positive protons pushing apart. When fission occurs: 1. Energy is produced. 2. Neutrons are released. Products of Fission are radioactive See pages 313-314
Nuclear Fission of Uranium-235 It is much easier to crash a neutral neutron than a positive proton into a nucleus to release energy. Most nuclear fission reactors and weapons use this principle. 1 n A neutron, 0, crashes into an atom of stable uranium-235 to create unstable uranium-236, which then undergoes radioactive decay. After several steps, atoms of krypton and barium are formed, along with the release of three neutrons and huge quantities of energy. The induced nuclear fission of uranium-235. This nuclear reaction is the origin of nuclear power and nuclear bombs. See pages 316-317
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Chain Reactions Once the nuclear fission reaction has started, it can keep going. The neutrons released in the induced reaction can then trigger more reactions on other uranium-235 atoms. Nuclear Chain Reaction. https://www.yout ube.com/watch? v=0v8i4v1mieu See page 318
This chain reaction can quickly get out of control. Fermi realized that materials that could absorb some neutrons could help to control the chain reaction. Materials like cadmium absorb neutrons to limit reaction Nuclear reactors have complex systems to ensure the chain reaction stays at safe levels. An uncontrolled chain reaction can result in a violent nuclear explosion. Nuclear bombs are created using this concept.
Nuclear power plants can generate large amounts of electricity. Ontario, Quebec and New Brunswick currently generate nuclear power. Canadian-made nuclear reactors are called CANDU reactors. CANDU reactors are considered safe and effective and are sold throughout the world. The Bruce Nuclear Generating Station on the shore of Lake Huron, in Ontario
CANDU Reactors and Hazardous Wastes Canada s nuclear research into the safe use of nuclear reactions has resulted in the creation of CANDU reactors. (Canadian deuterium uranium reactor) The reactors are known to be safe and easy to shut down in an emergency. Deuterium is an isotope of hydrogen which has one proton and one neutron ( Hydrogen-2) Reactors produce heat energy which turns electricity-generating turbines. Inside a CANDU reactor. https://www.youtube. com/watch?v=b4q9 O1vICWs See pages 319-320
Hazardous wastes produced by nuclear reactions are problematic. Some waste products, like fuel rods (contain uranium pellets), can be reused. Some products are very radioactive, however, and must be stored away from living things. Most of this waste is buried underground or stored in concrete. It will take 20 half-lives (thousands of years) before the material is safe.
Nuclear Fusion Nuclear fusion = joining of two light nuclei into one heavier nucleus. When the helium atom is formed, huge amounts of energy are released. It requires high temperatures. It occurs in the Sun and other stars. It does not produce radioactive materials. It is this energy that passes from the sun as radiation bringing light and heat to earth
Fusion on Earth? Scientists cannot yet find a safe, manageable method to harness the energy of nuclear fusion. So-called cold fusion would occur at temperatures and pressures that could be controlled.
Discussion Questions 1) Compare chemical reactions and nuclear reactions in terms of how much energy they transform. 2) a) What is a radioactive isotope? 3. How is alpha decay different from beta decay? 4. Compare Fission and Fusion
pages 140-141 of handout