# 006 - Lecture 6 Chemical Stoichiometry(Chapter 2...

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1 Lecture 6: Chemical Stoichiometry (Chapter 2) Stoichiometry - The study of quantities of materials consumed and produced in chemical reactions. The chemical engineer calls this " mass balances Concepts: mole, atomic mass unit (amu), empirical and molecular formulas, percentage composition, balanced equations and mass relationship in chemical reactions, reaction yield and limiting reagent.

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2 The Mole (review) The Mole is a counting unit: 1 dozen = 12 1 mole = 6.022137 x 10 23 The mole is defined as the number of atoms in exactly 12 g of 12 C The molar mass (atomic weight in g) is defined as the mass of one mole of that element The molar mass of an element is given by weighted average: naturally abundant C 98.89%(12.000)+1.11%(13.0034) 12.011 g 100%
3 Chemical Formulas Empirical formula: simplest formula that has the correct relative number of atoms in the molecule: C 4 H 9 Molecular formula : Formula with the correct number of atoms in the molecule. A multiple of the empirical formula C 8 H 18 Ionic formula : Empirical formulas for ionic solids NaCl

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4 Molar Mass A substance’s molar mass (molecular weight) is the mass in grams of one mole of the compound. Example: What is the molar mass of C 2 H 5 OH? C : 2 12.011 = 24.022 g H 6 1.0079 6.0474 g O 1 15.9994 15.9994 g Total : 46.069 g Molar mass of ethanol is 46.069 g/mol
5 Percent Composition in a Compound Mass percent of an element: mass% total mass of an element in a compound total mass of compound 100%

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6 Sample problem What is the % composition of C 2 H 5 OH?
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## This note was uploaded on 02/23/2010 for the course CHEM 115ALg at USC.

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006 - Lecture 6 Chemical Stoichiometry(Chapter 2...

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