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Chapter_04_Notes - Chapter 4 Chemical Quantities and...

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6/5/2010 1 Chapter 4 Chemical Quantities and Aqueous Reactions 1 4.2 Stoichiometry stoi·chi·om·e·try noun Literally – measuring the components Calculations of the quantitative relationships between reactants and products in a chemical reaction. All calculations are based on the limiting reagent, the one that is completely used up and thus limits the amounts of everything else. PDF Created with deskPDF PDF Writer - Trial :: http://www.docudesk.com
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6/5/2010 2 A. The Balanced Chemical Equation Representation of a chemical reaction which uses stoichiometric coefficients (prefix numbers) to represent the relative amounts of reactants and products 2 H 2 (g) + O 2 (g) 2 H 2 O (l) Molecule to Molecule or Mole to Mole Can use to calculate moles of one substance from moles of another B. The Mole and Chemical Reactions: The Macro-Nano Connection 2 H 2 + O 2 2 H 2 O 2 H 2 molecules 1 O 2 molecule 2 H 2 O molecules 2 moles H 2 molecules 1 mole O 2 molecules 2 moles H 2 O molecules •In this case both reactants run out together. •Hydrogen and oxygen are present in the stoichiometric ratio –The ratio determined by the reaction stoichiometry 4.0 g 32.0g 36.0g PDF Created with deskPDF PDF Writer - Trial :: http://www.docudesk.com
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6/5/2010 3 Stoichiometric Relationships grams of A moles of A moles of B grams of B molar mass of A molar mass of B mole ratio 2 A + C barb4right 3 B +D EXAMPLE How much iron(III) oxide and aluminum powder are required to field weld the ends of two rails together? Assume that the rail is 132 lb Fe/yard and that the weld is 1/10 inch wide. weld Fe 2 O 3 + Al barb4right Al 2 O 3 + Fe How much Fe 2 O 3 and Al is needed? PDF Created with deskPDF PDF Writer - Trial :: http://www.docudesk.com
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6/5/2010 4 The mass of iron in 1/10 inch of this rail is: g lb g yd lb in yd in 166 1 454 1 132 36 1 10 1 = × × × Fe 2 O 3 + 2 Al Al 2 O 3 +2 Fe 3 2 3 2 3 2 3 2 O Fe g 237 O Fe mol 1 O Fe g 68 . 159 Fe mol 2 O Fe mol 1 Fe g 84 . 55 Fe mol 1 Fe g 166 = × × × Fe needed The bottles of wine example Must make 2-liter bottles or wine Each bottle needs 1 cork, 1 bottle and 2 liters of wine We have 3 corks, 3 bottles, and 4 liters of wine How many 2-liter bottles of wine can be made (theoretical yield)? What is the limiting reagent? 1 liter of wine lost accidently, so only one 2-liter bottle of wine actually made, what is percent yield? 8 4.3 Limiting Reactant, Theoretical Yield and Percent Yield PDF Created with deskPDF PDF Writer - Trial :: http://www.docudesk.com
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6/5/2010 5 A. Limiting Reactant in Chemical Reactions In a chemical reaction, if you are not told that one species is limiting then you need to determine the limiting reactant by either, 1. Comparing available moles of reactants to the required moles or 2. Determining which reactant gives the smallest amount of product (in moles or in grams) What is the number of moles of CaSO 4 that can be produced by allowing 1.0 mol SO 2 , 2.0 mol CaCO 3 , and 3.0 mol O 2 to react?
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