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PAGE 7-1 ANSWERS TO END-OF-CHAPTER QUESTIONS CHAPTER 7: THE FIRES OF NUCLEAR FISSION Emphasizing Essentials 1 . Give two ways in which an atom of carbon can differ from another atom of carbon. Then give three ways in which all carbon atoms differ from all uranium atoms. Answer: One carbon atom can differ from another in the number of neutrons (such as C-12 and C-13) and in the number of electrons (we won’t be studying carbon ions, but these do exist). All carbon atoms differ from all uranium atoms in their number of p, n and e and also in their chemical properties. 2 . Representations such as 14 N or 15 N give more information than simply the atomic symbol N. Explain. Answer: The symbol N represents the element nitrogen and stands for the naturally occurring mixture of all isotopes. The symbols 14 N and 15 N represent very specific isotopes with mass numbers of 14 and of 15, respectively. 3 . a. How many protons does an atom of 94 239 Pu contain? b. What element contains one more proton than uranium? Two more? c. How many protons does radon-222 contain? Answer: a. 94 protons b. Np (neptunium), Pu (plutonium) c. 86 protons 4 . Determine the number of protons and neutrons in each of these nuclei. a. C-14 (radioactive) b. C-12 (stable) c. H-3 (tritium, a radioisotope of hydrogen) d. Tc-99 (a radioisotope used in medicine) Answer: a. C-14 has 6 protons and 8 neutrons b. C-12 has 6 protons and 6 neutrons c. H-3 has 1 proton and 2 neutrons d. Tc-99 has 43 protons and 56 neutrons
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PAGE 7-2 5 . E = mc 2 is one of the most famous equations of the 20th century. What do the symbols in the equation represent? Answer: E represents energy, m represents mass lost in a nuclear transformation, and c represents the speed of light. 6 . Give an example of a nuclear equation and of a chemical equation. In what ways are the two equations alike? Different? Answer: Nuclear equation: Chemical equation: CH 4 + 2 O 2 CO 2 + 2 H 2 O In a chemical equation, the elements do not change their identities in the process of being converted from reactants to products. Even though they are combined differently, the same number of atoms of each kind must appear on both sides of the equation. Usually only the symbols for the elements are given, not their atomic or mass numbers. In a nuclear equation, the identity of the elements may change, or at least the mass number may change. The values for both the atomic and mass numbers are often included. 7 . This nuclear equation represents a plutonium target being hit by an alpha particle. Show that the sum of the subscripts on the left is equal to the sum of the subscripts on the right. Then do the same for the superscripts. Answer: Subscripts: 94 + 2 = 96 on the left, 96 + 0 = 96 on the right Superscripts: 239 + 4 = 243 on the left; 242+1=243 on the right 8 . For the nuclear equation shown in the previous question, a. suggest how the 2 4 He was produced.
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This note was uploaded on 07/02/2011 for the course CHEM-C 118 taught by Professor Flood during the Spring '10 term at Indiana.

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