Stoichiometry Calculations with Chemical Formulas and Equations
Chapter 3 BLB 12 th
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Expectations Balance chemical equations. Balance chemical
equations. g moles molecules atoms g moles molecules atoms Find
empirical and molecular problems. Find empirical and molecular
problems. Calculate amounts of reactants and products. Calculate
amounts of reactants and products. Calculate theoretical and
percent yield. Calculate theoretical and percent yield.
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Stoichiometry Quantity relationships based on chemical
equations 3 Main Concepts: 1. 1. Chemical formula molar ratio of
atoms 2. 2. Chemical equations molar ratio of compounds 3. 3. Law
of Conservation of Mass: mass of reactants = mass of products
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3.1 Chemical Equations Components: reactants products Physical
states (s, l, g, aq) Reaction conditions (heat , light, solvents,
etc.) Coefficients determine molar ratios. The number of moles of
each type of atom must be the same on each side. Balancing: By
inspection Use coefficients; dont change chemical formulas
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Coefficients vs. Subscripts
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Fe 2 S 3 (s) + HCl(aq) FeCl 3 (s) + H 2 S(g) KClO 3 (s) KCl(s)
+ O 2 (g) HNO 3 (l) + P 4 O 10 (s) (HPO 3 ) 3 (l) + N 2 O 5
(g)
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3.2 Some Simple Patterns of Chemical Reactivity Combination and
Decomposition combination: A + B C 4 Fe(s) + 3 O 2 (g) 2 Fe 2 O 3
(s) decomposition: C A + B 2 NaN 3 (s) 2 Na(s) + 3 N 2 (g)
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3.2 Some Simple Patterns of Chemical Reactivity Combustion
burning of a fuel in the presence of oxygen products of complete
combustion: CO 2, H 2 O exothermic (produces heat)
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Molecular view of methane combustion
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3.2 Some Simple Patterns of Chemical Reactivity Combustion C 3
H 8 (g) + 5 O 2 (g) 3 CO 2 (g) + 4 H 2 O(g) 2 CH 3 OH(g) + 3 O 2
(g) 2 CO 2 (g) + 4 H 2 O(g) Each C atom in fuel produces 1 mol CO 2
Each H atom in fuel produces mol H 2 O
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3.3 Formula Weights Formula and Molecular Weights (amu) formula
weight general molecular weight molecules formula unit weight ionic
compound - sum of the atomic masses of each atom in chemical
formula
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% Composition % composition by mass % composition by mass Mass
of one type of atoms over mass of all atoms Mass of one type of
atoms over mass of all atoms
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3.4 Avogadros Number and the Mole Word association: Word
association: pair dozen case ream
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amu impractical for lab use (too small) Avogadros number:
6.0221421 x 10 23 mol -1 The number of atoms in exactly 12 g of 12
C For conversions: 6.022 x 10 23 ?/mol, where ? can equal atoms,
molecules, ions, etc. 1 mole = Avogadros number of anything molar
mass mass in grams of one mole of a substance, which is equal to
the atomic mass in amu; g/mol 3.4 Avogadros Number and the
Mole
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Atoms & compounds have different masses, thus the mass of 1
mole of atoms & compounds are different. 3.4 Avogadros Number
and the Mole
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Conversions: g mol divide by molar mass mol g multiply by molar
mass Abbreviations:mole mol molarity M 3.4 Avogadros Number and the
Mole
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Practice with Avogadros # & the Mole
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3.5 Empirical Formulas from Analyses Empirical formula
Empirical formula smallest whole number ratio of atoms Molecular
formula Molecular formula actual ratio of atoms in a compound;
multiple of the empirical formula; must know molar mass of compound
Use % composition to find formulaProblems
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A once-used gasoline additive contains 49.5% C, 3.2% H, 22.0%
O, and 25.2% Mn. Determine the emipirical formula of this
compound.
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Azulene, a hydrocarbon, contains 93.71% C. Its molar mass is
~128 g/mol. Determine the emipirical and molecular formulas for
azulene.
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3.5 Empirical Formulas from Analyses Summary: % data grams
Grams moles Moles molar ratio empirical formula Empirical formula
molecular formula
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3.5 Empirical Formulas from Analyses Combustion analysis
Combustion analysis 1 mol C in fuel 1 mol CO 2 2 mol H in fuel 1
mol H 2 OProblems
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The combustion of propane, a hydrocarbon, produces 2.641 g CO 2
and 1.442 g H 2 O. Determine the emipirical formula of
propane.
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3.6 Quantitative Information from Balanced Equations 3 Main
Concepts: 1. 1. Chemical formula molar ratio of atoms 2. 2.
Chemical equations molar ratio of compounds 3. 3. Law of
Conservation of Mass: mass of reactants = mass of products
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Whats balanced in a balanced equation?
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Stoichiometry Problems Use these 4 steps as a guide: (p. 97)
Write & balance chemical equation. Convert to moles. Apply
molar ratio. Convert from moles to quantity desired (mass, volume,
etc.)
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Stoichiometry Problems
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How many grams of CaCl 2 is produced from taking 2 antacid
tablets, each containing 500. mg of CaCO 3 ? CaCO 3 (s) + 2 HCl(aq)
CO 2 (g) + H 2 O(l) + CaCl 2 (s)
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From Sample Exercise 3.16, p. 98
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How many grams of HCl are needed to react with 1000 mg of CaCO
3 ? CaCO 3 (s) + 2 HCl(aq) CO 2 (g) + H 2 O(l) + CaCl 2 (s)
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3.7 Limiting Reactants Limiting reactant reactant that is
completely consumed; limits the amount of product that can be
formed Theoretical yield calculated yield of a product based on
limiting reactant Percent yield
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78. Calculate the theoretical yield (in grams) of NO when 2.00
g of NH 3 react with 2.50 g of O 2. NH 3 (g) + O 2 (g) NO(g) + H 2
O(g)
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Silver metal reacts with elemental sulfur according to the
reaction below. If 2.0 g each of silver and sulfur react, what is
the theoretical yield (in grams) of silver(I) sulfide? How many
grams are left over? 16 Ag(s) + S 8 (s) 8 Ag 2 S(s)
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How many grams are left over? 16 Ag(s) + S 8 (s) 8 Ag 2 S(s) 16
Ag(s) + S 8 (s) 8 Ag 2 S(s)
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84. When hydrogen sulfide gas is bubbled into a solution of
sodium hydroxide, the reaction forms sodium sulfide and water. How
many grams of sodium sulfide are formed if 1.25 g of hydrogen
sulfide is bubbled into a solution containing 2.00 g of sodium
hydroxide, assuming that the sodium sulfide is made in 92.0%
yield?
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When 0.750 g iron(III) chloride hydrate is heated, 0.300 g of
steam is produced. What is the value of x ? FeCl 3 x H 2 O(s) FeCl
3 (s) + x H 2 O(g)
