UT Knoxville CHEM 120 - Chapter 3 Lecture Outline (13 pages)

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Chapter 3 Lecture Outline



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Chapter 3 Lecture Outline

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Pages:
13
School:
University of Tennessee
Course:
Chem 120 - General Chemistry I
General Chemistry I Documents

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1 Chapter 3 Stoichiometry Chemical Calculations 3 1 Lecture Outline CHEMICAL EQUATIONS A chemical equation tells a story Balancing Equations the number of atoms of each elements must be the 1 Balancing atoms which occur in only one compound on each side 2 Balance free elements last 3 Balance unchanged polyatomic ions as a unit 4 Do NOT change subscripts 5 Recheck Balance the following C4H10 O2 C CO2 H2O Practice exercise 3 2 Balance each of the following equations 3 2 Fe s O2 g Al s HCl g Types of Reactions Combination Reactions Two or more substances react to form one product For example 2 Mg s O2 g N2 g 3 H2 g C3H6 g Br2 l 2 MgO s 2 NH3 g C3H6Br2 l Fe2O3 s AlCl3 H2 g 2 Decomposition Reactions In a decomposition reaction one substance breaks down into two or more substances For example CaCO3 s 2 KClO3 s 2 NaN3 s CaO s CO2 g 2 KCl s O2 g 2 Na s 3 N2 g Combustion in Air Is the burning of a compound in air It most often involves hydrocarbons reacting with oxygen in the air to produce CO2 and H2O For example CH4 g 2 O2 g C3H8 g 5 O2 g CO2 g 2 H2O g 3 CO2 g 4 H2O Examples Write balanced equations for each of the following reactions a Solid mercury II sulfide decomposes into its component elements when heated b The surface of aluminum metal undergoes a combination reaction with oxygen in air c Write the balanced equation for the reaction that occurs when ethanol C2H5OH l is burned in air 3 3 FORMULA WEIGHT FW of a substance is the sum of atomic weights for the atoms in a chemical formula generally reported for ionic compounds So the formula weight of calcium chloride would be 3 MOLECULAR WEIGHT MW is the sum of the atomic weights of the atoms in a molecule generally reported for molecular compounds So the molecular weight of ethane would be PERCENT COMPOSITION Mass Percentages from Formulas consider Al OH 3 calculate formula weight Calculate percentages Al x 100 O H Practice problem What is the percentage of H in acetic acid HC2H3O2 3 4 MOLE AND AVOGADRO S NUMBER Mole is



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