Ch04 MSJ jlm - Chapter 4 Quantities of Reactants and...

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1 Quantities of Reactants and Quantities of Reactants and Products Products Chapter 4 Chapter 4 Antoine Lavoisier 1743-1794. “Father of modern chemistry.” Recognized true elements. Used quantitative measurements in chemical reactions.
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2 Lavoisier: mass is conserved in a chemical reaction. Chemical equations: descriptions of chemical reactions. Two parts to an equation: reactants and products : Chemical Equations Chemical Equations 2H 2 + O 2 2H 2 O Reactants Product
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3 H 2 O 2 H 2 O
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4 Stoichiometric coefficients : numbers in front of the chemical formulas give numbers of molecules or atoms reacting (and numbers being produced).
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5 CH 4 + O 2 CO 2 + H 2 O Count atoms: Reactants : Products : 1 C 1 C 4 H 2 H 2 O 3 O is not balanced. (Why?) Law of Conservation of Mass: All reactions must be balanced
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6 Balance reactions only by changing coefficients, not by altering chemical formula
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7 Combustion is the burning of a substance in oxygen:
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8 Which is correct? (Blue=A; Red=B) a) A 2 + B A 2 B b) A 2 + 4B 2 AB 2 c) 2A + B 4 2 AB 2 d) A + B 2 AB 2
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9 Percentage Composition from Formulas Percentage Composition from Formulas Percent composition is the atomic weight for each element divided by the formula weight of the compound multiplied by 100: Atomic and Molecular Weights Atomic and Molecular Weights ( 29 ( 29 100 Compound of FW AW Element of Atoms Element % × =
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10 Percentage Composition from Formulas Percentage Composition from Formulas FW= (2x1) + (1x32)+ (4x16)= 98 amu FW of O in H 2 SO 4 = 4 x 16 = 64 amu What is % O in H 2 SO 4 (by mass)? %O = 64 x 100 = 65.3% 98
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11 The Mole* The Mole* The “amu” is an “atomic mass unit.” O has a mass of 16 amu – but we can’t weigh out anything in amu If we want to keep the number “16” for the mass of oxygen in some real units (like grams ) then we are dealing with a whole bunch of atoms (in 16 g of oxygen). That bunch of atoms is called a
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This note was uploaded on 04/12/2011 for the course CHEM 1420 taught by Professor Acree during the Spring '08 term at North Texas.

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Ch04 MSJ jlm - Chapter 4 Quantities of Reactants and...

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