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3 Stoichiometry

# 3 Stoichiometry - Chapter 3 Stoichiometry Calculations with...

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1 Chapter 3 Stoichiometry: Calculations with Chemical Formulas and Equations Chemical Equations H 2(g) O 2(g) H 2 O(l) + 2 2 Reactants Product(s) Coefficients State of reatants and products 2

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2 Example: Balance the following reactions N 2(g) H 2(g) NH 3(g) + 2 3 C 5 H 12 O 2(g) CO 2 + + H 2 O 6 5 8 KClO 3(s) KCl (s) + O 2 3 2 2 Reaction Types Combination Reactions Two or more substances react to form one product A + B C •Examples: CaCO 3 ( s ) → CaO ( s ) + CO 2 ( g ) •Examples: N 2 ( g ) + 3 H 2 ( g ) → 2 NH 3 ( g ) C One substance breaks down into two or more substances A B + Decomposition Reactions 4
3 Reaction Types (cont) Combustion Reactions Most often involve hydrocarbons reacting with oxygen in the air •Example: CH 4 ( g ) + 2 O 2 ( g ) → CO 2 ( g ) + 2 H 2 O ( g ) Formula Weights or Molecular weights Sum of the atomic weights for the atoms in a chemical formula Example : the formula weight of calcium chloride, CaCl 2 , would be: Ca: 1(40.1 amu) + Cl: 2(35.5 amu) 111.1 amu 6

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4 H 2 O (1x2) + (16x1) = 18 amu C 3 H 9 N (12x3) + (1x9) + (14x1) = 59 amu C 6 H 12 O 6 (12x6) + (1x12) + (16x6) = 180 amu Example: Calculate the formula weight of the following compounds: Percent Composition One can find the percent composition by using this equation: % element = (number of atoms)(atomic weight) (FW of the compound) x 100 E x a m p l e : Calculate the percent composition by mass of each element in H 2 O 2 .
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