And to convert energy to matter observed in creation

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Unformatted text preview: nd fission), and to convert energy to matter (observed in creation of elementary particles). • It is important to note here the law of conservation of mass, which embodies in it the principles that both matter and energy are conserved. In essence, it says that the mass to be conserved includes both the mass of the matter in the system (portion of the universe that is singled out for study) and the mass of energy in the system. Sample Problem 1.5: Einstein’s relation between mass and energy: nuclear reaction. When 1 kg of uranium 235 (235U) undergoes nuclear fission, as in the detonation of an atomic bomb, 0.823 × 1014J of energy is liberated. How much has the mass of sample decreased? Let’s calculate the mass of uranium lost by the use of Einstein’s equation E 0.823 × 1014 J m= 2 = = 0.0916 × 10− 2 kg = 0.000916 kg c (2.998 × 108 ) 2 m 2 s − 2 Thus, the mass of 235U has decreased by 0.0916%. In the above example, a small amount of matter was converted to a large amount of energy. But that mass lost is relatively large compared to mass lost in non-nuclear reactions – reactions that we’re concerned with in general chemistry. Let’s take a very explosive reaction and see how much mass is lost in the process. Sample Problem 1.6: Einstein’s relation between mass and energy: non-nuclear reaction. When 1 kg of nitroglycerine explodes, 8.0 × 106 J of energy is liberated. How much has the mass of sample decreased? Let’s calculate the mass of nitroglycerine lost by the use of Einstein’s equation 0.823 × 106 J E m= 2 = = 0.89 × 10−10 kg = 0.000000000089kg (2.998 × 108 ) 2 m 2 s − 2 c Thus, the mass of nitroglycerine has decreased by 0.0000000089%. From the above example we see that the difference in mass of the product and reactants in non-nuclear reactions is negligible. In fact, it is so slight that you would never detect it with regular weight balances. For all practical purposes, we say that mass of matter is conserved in ordinary chemical reactions. Effectively, for ordinary chemical reactions we can ignore the energy part, and simply say that the total mass of the products of chemical reaction is the same as the total mass of reactants. Mass of matter is conserved in ordinary chemical reactions. 19 Copyright © 2007 by Concise Books Publishing LLC. Visit us at www.concisechem.com to download other free chapters from "The Concise Guide to Chemistry." CHAPTER 1: INTRODUCTION TO CHEMISTRY Section Test Questions 1. Loss of mass is an important factor in: (a) nuclear reactions, (b) ordinary reactions, (c) both? Answers 1. A - see sample problems 1.5 and 1.6. Antimatter, Dark Matter & Dark Energy 1.5 You’ve probably heard of, if not even read, Dan Brown’s bestselling fiction novel Angels and Demons in which he talks about a plot to destroy the Vatican using 1 gram of antimatter stolen from Switzerland’s Conseil Europeen pour la Recherche Nucleaire (CERN). Luckily, antimatter is not present in the universe...
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This document was uploaded on 09/19/2013.

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