Modern Chemistry Chapter 9 Stoichiometry

1
Modern ChemistryChapter 9Stoichiometry
Sections 1-3Introduction to StoichiometryIdeal
Stoichiometric CalculationsLimiting Reactant and
Percent Yield
2
Definitions

• Composition stoichiometry deals with the mass
  relationships of elements in compounds.
• Reaction stoichiometry involves the mass
  relationships between reactants and products in a
  chemical reaction.

3
Definitions

• A mole ratio is a conversion factor that relates
  the amounts in moles of any two substances
  involved in a chemical reaction
• Example 2Al2O3(l) ? 4Al(s) 3O2(g)
• Mole Ratios 2 mol Al2O3 2 mol Al2O3
  4 mol Al
• 4 mol Al 3 mol O2 3 mol O2

4
Mole Mole Examples

• Mg(s) 2HCl(aq) ? MgCl2(aq) H2(g)
• If 2 mol of HCl react, how many moles of H2 are
  obtained?
• How many moles of Mg will react with 2 mol of
  HCl?
• If 4 mol of HCl react, how many mol of each
  product are produced?
• How would you convert from moles of substances to
  masses?

5
Section 1 Homework
Page 301 1-4
Chapter 9 Section 1 Intro. Stoichiometry pages
299-303
6
Chapter 9 Section 2Ideal Stoichiometric
Calculations
Chapter 9 Section 2 Ideal Stoichiometry pages
304-311
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Reactants ? Products
MASS OF SUBSTANCEGIVEN
MASS OF SUBSTANCEWANTED
MOLAR MASS
MOLAR MASS
MOLES OF SUBSTANCEGIVEN
MOLES OF SUBSTANCEWANTED
MOLE RATIO
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Tool Box
GRAMS?mL DENSITY
GRAMS?MOLES MOLAR MASS
MOLES ?MOLES MOLE RATIO
MOLES ?PARTICLES 6.02x1023
1000 g 1kg
1000 mL 1L
1000 mg 1g
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Kg
L
mg
mL
g
MOLES
MOLES
g
mg
mL
L
Kg
10
Sample Problem
How many kilograms of ethane are required to
react with excess oxygen to produce 8.70 L of
carbon dioxide? The density of carbon dioxide gas
at standard temperature is 1.799 g/L.
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Kg
L
mg
mL
g
MOLES
MOLES
g
mg
mL
L
Kg
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2C2H6 (g) 7O2 (g) ? 4CO2 (g) 6H2O (g) E
g
g
MOLES
MOLES
L CO2
g CO2
mol C2H6
kg C2H6
mol CO2
g C2H6
x
x
x
x
x
L CO2
g CO2
mol CO2
mol C2H6
g C2H6
13
C2H6 (g) O2 (g) ? CO2 (g) H2O (g) E
g
g
1000g1Kg
MOLAR MASS
MOLAR RATIO
MOLAR MASS
MOLES
MOLES
DENSITY
L CO2
g CO2
mol C2H6
kg C2H6
mol CO2
g C2H6
x
x
x
x
x
L CO2
g CO2
mol CO2
mol C2H6
g C2H6
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Sample Problem p. 306
In photosynthesis, plants use energy from the sun
to produce glucose, C6H12O6, and oxygen from the
reaction of carbon dioxide and water. What
mass, in grams, of glucose is produced when 3.00
mol of water react with carbon dioxide?
mol-mass
15
Sample Problem p. 310
Tin (II) fluoride, SnF2, is used in some
toothpastes. It is made by the reaction of tin
with hydrogen fluoride according to the following
equation. Sn(s) 2HF(g) ? SnF2(s) H2(g)
How many grams of SnF2 are produced from the
reaction of 30.00 g HF with Sn?
mass-mass.
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Sample Problem p. 305

• In a spacecraft, the carbon dioxide exhaled by
  astronauts can be removed by its reaction with
  lithium hydroxide, LiOH, according to the
  following chemical equation.
• CO2(g) 2LiOH(s) ? Li2CO3(s) H2O(l)
• How many moles of lithium hydroxide are required
  to react with 20 mol CO2, the average amount
  exhaled by a person each day?

mol-mol
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Sample Problem p. 309
The first step in the industrial manufacture of
nitric acid is the catalytic oxidation of
ammonia. NH3(g) O2(g) ? NO(g) H2O(g)
(unbalanced) The reaction is run using 824 g
NH3 and excess oxygen. a. How many moles of NO
are formed? b. How many moles of H2O are formed?
mass-mol
18
Problem
Magnesium burns in oxygen to produce magnesium
oxide. How many grams magnesium will burn in the
presence of 189 mL of oxygen? The density of
oxygen is 1.429g/L.
mL-g
19
Problem
Limestone, CaCO3, can be decomposed with heat to
form lime, CaO, and carbon dioxide. How many
moles of lime would be formed from the
decomposition of 20.1 kilograms of limestone?
Kg-mol.
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Section 2 Homework
Page 311 1-5
Chapter 9 Section 2 Ideal Stoichiometry pages
304-311
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Section 2 HomeworkProblem Bank
Page 890-892 176, 177, 179, 180, 184, 187, 190,
191, 192, 194, 196
Chapter 9 Section 2 Ideal Stoichiometry pages
304-311
22
Chapter 9 Section 3Limiting Reactant and Percent
Yield
Chapter 9 Section 3 Limiting Reactant pages
312-318
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Definitions

• The limiting reactant is the reactant that limits
  the amount of the other reactant that can combine
  and the amount of product that can form in a
  chemical reaction.
• The excess reactant is the substance that is not
  used up completely in a reaction.

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Smores

• Given the bag o reactants find the number of
  smores you could produce if the balanced
  equation is
• 2 Ac 1 Ma 1Mm ? 1 Sm
• Ac Animal Cracker
• Ma Minimarshmallow
• Mm M M
• Sm Smore

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Smores

• What is the limiting reactant?
• What is the reactant in excess?
• What is the amount in excess ?
• What is the theoretical yield?
• What is the actual yield?
• What is the percent yield?

Chapter 9 Section 3 Limiting Reactant pages
312-318
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Sample Problem p. 313
Silicon dioxide (quartz) is usually quite
unreactive but reacts readily with hydrogen
fluoride according to the following equation.
SiO2(s) 4HF(g) ? SiF4(g) 2H2O(l) If 6.0
mol HF is added to 4.5 mol SiO2, which is the
limiting reactant?
mol mol limiting
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Problem
I need a problem that requires them to answer
these questions a. Which compound is the
limiting reactant? b. What is the theoretical
yield of product? c. What is the reactant in
excess, and how much remains after the reaction
is completed?
mass mass, limiting, actual
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Problem
I need another problem that requires them to
answer these questions a. Which compound is the
limiting reactant? b. What is the theoretical
yield of product? c. What is the reactant in
excess, and how much remains after the reaction
is completed?
mass mass, limiting, actual
29
Section 3 Homework
Page 318 1 2
Chapter 9 Section 3 Limiting Reactant pages
312-318
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Definitions

• The theoretical yield is the maximum amount of
  product that can be produced from a give amount
  of reactant.
• The actual yield is the measured amount of
  product obtained from a reaction.
• The percentage yield is the ratio of the actual
  yield to the theoretical yield, multiplied by 100.

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Sample Problem p. 317
Chlorobenzene, C6H5Cl, is used in the production
of many important chemicals, such as aspirin,
dyes, and disinfectants. One industrial method of
preparing chlorobenzene is to react benzene,
C6H6, with chlorine, as represented by the
following equation. C6H6 (l) Cl2 (g) ?
C6H5Cl (l) HCl (g) When 36.8 g C6H6 react
with an excess of Cl2, the actual yield of C6H5Cl
is 38.8 g. What is the percentage yield of
C6H5Cl?
mass-mass percent
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Problem
Hydrogen sulfide gas can be formed by the action
of HCl and FeS, forming FeCl2 as product. What
is the theoretical yield in molecules of
hydrogen sulfide if 130.5 g of FeS are mixed with
150.0 g of HCl? If the percent yield in the lab
is 93.6 what is the actual yield?
mass mass, limiting, actual
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Problem
Benzene, C6H6, is reacted with bromine, Br2, to
produce bromobenzene, C6H5Br, and hydrogen
bromide, HBr, as shown below. When 40.0 g of
benzene are reacted with 95.0 g of bromine, 65.0
g of bromobenzene is produced. C6H6 Br2 ?
C6H5Br HBr a. Which compound is the limiting
reactant? b. What is the theoretical yield of
bromobenzene? c. What is the reactant in excess,
and how much remains after the reaction is
completed? d. What is the percentage yield?
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Molarity

• Molarity measures the concentration of solutions.
  (aq)
• Molarity moles / liter

3 mol
3M
1 L
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Problem
When 20.0 mL of 0.90M solution of lithium nitrate
and 15.0 mL of 0.40M solution of calcium
phosphate react, a precipitate is formed. The
mass of the precipitate produced in the lab is
0.66 grams. What is the reactant in excess, the
limiting reactant, the amount in excess, the
theoretical yield and the percent yield.
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Section 3 HomeworkProblem Bank
Page 892-894 201, 208, 214, 217, 219, 223, 226,
229, 232
Chapter 9 Section 3 Limiting Reactant pages
312-318