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Chem 101 Chapter 4- Chemical Equations and Stoichiometry

Chem 101 Chapter 4- Chemical Equations and Stoichiometry -...

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Black Smokers and the Origin of Life “The origin of life appears almost a miracle, so many are the conditions which would have had to be satisfied to get it going.” Francis Crick, quoted by John Horgan, “In the Beginning,” Scientific American, pp. 116–125, February 1991. The statement by Francis Crick on the origin of life does not mean that chemists and biologists have not tried to find the conditions under which life might have begun. Charles Darwin thought life might have begun when simple molecules combined to produce molecules of greater and greater complexity. Darwin‘s idea lives on in experiments such as those done by Stanley Miller in 1953. At- tempting to recreate what was thought to be the atmosphere of the primeval earth, Miller filled a flask with the gases methane, ammo- nia, and hydrogen and added a bit of water. A discharge of electric- ity acted like lightning in the mixture. The inside of the flask was soon covered with a reddish slime, a mixture found to contain amino acids, the building blocks of proteins. Chemists thought they would soon know in more detail how living organisms began their develop- ment—but it was not to be. As Miller said recently, “The problem of the origin of life has turned out to be much more difficult than I, and most other people, envisioned.” Other theories have been advanced to account for the origin of life. The most recent conjecture relates to the discovery of geologi- cally active sites on the ocean floor. Could life have originated in such exotic environments? The evidence is tenuous. As in Miller‘s experiments, this hypothesis relies on the creation of complex carbon-based molecules from simple ones. In 1977 scientists were exploring the junction of two of the tectonic plates that form the floor of the Pacific Ocean. There they 4 Chemical Equations and Stoichiometry National Oceanic and Atmospheric Administration/Department of Commerce The Basic Tools of Chemistry A “black smoker” in the East Pacific Rise. 140
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141 Chapter Outline 4.1 Chemical Equations 4.2 Balancing Chemical Equations 4.3 Mass Relationships in Chemical Reactions: Stoichi- ometry 4.4 Reactions in Which One Reactant Is Present in Limited Supply 4.5 Percent Yield 4.6 Chemical Equations and Chemical Analysis Chapter Goals See Chapter Goals Revisited (page 165). Test your knowl- edge of these goals by taking the exam-prep quiz on the General ChemistryNow CD-ROM or website. Balance equations for simple chemical reactions. Perform stoichiometry calculations using balanced chemi- cal equations. Understand the meaning of a limiting reactant. Calculate the theoretical and percent yields of a chemical reaction. Use stoichiometry to analyze a mixture of compounds or to determine the formula of a compound.
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