POGIL: Fission Fusion

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1 Name: Date: Period: Chemistry POGIL: Fission Fusion Why? Up until the 9 s, the only nuclear reactions that had been observed involved nuclei either capturing or emitting small particles such as alpha and beta particles. With Chadwick s discovery of the neutron a new area of experimentation began, the results of which were extremely peculiar. In 98, Otto Hahn and Fritz Strassmann experimented by bombarding uranium with neutrons and unexpectedly detected barium in the products. This didn t make sense, because adding neutrons to the uranium atoms should have increased their mass, but barium has a mass that is 4% less than that of uranium. According to their results, bombarding uranium with neutrons had led to the atoms splitting nearly in half. A whole new world of research opened up. Success Criteria Complete nuclear equations, and identify the missing products or reactants. Determine if a nuclear reaction is a transmutation, fission, or fusion reaction. Prerequisites Structure of atoms and isotopes. Atomic symbols including mass number, atomic number, and charge. Symbols for particles involved in transmutation equations. p, e e 4 He o n,,, Completing transmutation reactions and identifying the missing products or reactants. Vocabulary Nuclide = atomic nucleus with a specified numbers of protons and neutrons Transmutation = the conversion of an atom of one element to an atom of another element Fission = the splitting of a nucleus into smaller fragments Fusion = the process of combining nuclei to produce a nucleus of greater mass Information Transmutation is the transformation of the nucleus of an atom so that the atom changes from one element into a different element. This can be accomplished through many types of nuclear reactions, including fission and fusion. Regardless of the reactants and products, nuclear transformations always obey two fundamental conservation laws: conservation of mass number, and conservation of nuclear charge. Energy and mass are not conserved, but can be inter-converted according to Einstein s equation, E = mc, where energy is equal to the mass of an object multiplied by the speed of light squared. In nuclear reactions, energy is given off during the formation and splitting of a nucleus. Because of the large binding energies holding a nucleus together, nuclear reactions involve energy changes more than a million times larger than those associated with chemical reactions.

2 Model : Fission of Uranium Fission is the process by which a nucleus splits into smaller pieces. Fission can be induced by bombarding a nucleus with a neutron, causing it to become unstable. (Remember the band of stability where the proton and neutron ratio determine nuclear stability. Very few nuclei combinations are stable.) The unstable nucleus splits into nuclei of smaller mass U + n U (unstable) Ba + Kr + n Example reactions: U + n 6Nd + Ge + n U + n 5Sn + 4Mo + n 8 U + n Xe + 95 Sr + n What is used to trigger the fission reaction? How does it trigger the reaction?. How does the size of the reacting nucleus compare to the sizes of the product nuclei?. Why are all the above example reactions viable for the fission of uranium-5? 4. What is always conserved in nuclear transformations? 5. Given a starting nuclide of unranium-5, is it possible to predict the exact fission products for this isotope? Why?

3 Model : Fusion Fusion occurs when two nuclei join together to form a larger nucleus. Fusion is brought about by bringing together these nuclei under conditions of tremendous pressure and heat. Stars are the main source of fusion energy in the universe, and technically are not burning. (If they were undergoing combustion reactions, their fuel sources would only last for thousands of years.) Main sequence stars will undergo fusion of elements up to iron, at which point they will enter the nova or supernova stage of their life cycle. There is an intense race today to develop a feasible form of fusion since light nuclei are readily available. Unfortunately, the amounts of heat and radiation produced by these reactions are hard to control and contain. H + H 4 He + n. What are the other names for hydrogen- and hydrogen-? How are these isotopes different from hydrogen-?. Explain how each of the following is an example of a fusion reaction. 4 A. He + He He + H 4 B. He + H He + e C. Cf + O Sg + n

4 Model : Fission Chain Reactions Neutrons released during a fission reaction may strike surrounding nuclei, causing them to become unstable. These nuclei will then undergo the process of fission, releasing more neutrons into the sample. There is an enormous amount of energy released during these reactions. For instance, kg of uranium-5 can yield the same amount of energy as, tons (8,, kg) of dynamite. First Generation Second Generation. How many neutrons are given off after the first fission reaction?. How many uranium-5 atoms are triggered after the first fission reaction?. How many uranium-5 atoms will be triggered after the second generation of fission reactions? 4. How many uranium-5 atoms will be triggered after the third generation of fission reactions?

5 Exercises. Describe how to identify the missing species in the equation. 5 U + n 5 6 Nd + + n. An atom of uranium-5 absorbs a neutron and produces an atom of antimony-5 and four neutrons. Identify the other nuclide formed in this reaction. Write the equation to support your answer.. Identify the following equations as fission or fusion. Explain your choice. A. H + H H + e B. U + n Te + Zr + n 8 46 C. U + C Cf + 4 n D. Pa + n Ba + Br + n 4 E. 4 H He + e F. Np + n I + Br + n