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Chapter 9
Stoichiometry
Stoichiometry
• Composition stoichiometry
– Mass relationships of elements in
compounds
• Reaction stoichiometry
– Mass relationships between
reactants and products
Reaction Stoichiometry
• Use ratios from balanced
equation
• Problem Type 1
– Given & unknown quantities in
moles
• Problem Type 2
– Given in moles & unknown in grams
Reaction Stoichiometry
• Problem Type 3
– Given in grams & unknown in
moles
• Problem Type 4
– Given in grams & unknown in
grams
Mole Ratio
• Conversion factor that relates
amount of moles of substances
2Al2O3(l)  4Al(s) + 3O2(g)
• How many moles of aluminum
can be produced from 13.0 mol
of aluminum oxide?
Molar Mass
• The mass (in g) of 1 mole of
substance
2Al2O3(l)  4Al(s) + 3O2(g)
• How many grams of Al is
equivalent to 26.0 mol Al?
Conversions
• Problem Type 1
– Mole to mole
– One conversion factor: mole ratio
• Given (mol) x mole ratio
(mol/mol) = unknown (mol)
Conversions
• In a spacecraft, the CO2 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 LiOH are required to
react with 20 mol of CO2, the average
amount exhaled by a person each day?
Conversions
• The disinfectant hydrogen
peroxide, H2O2, decomposes to
form water and oxygen gas.
How many moles of O2, will
result from the decomposition
of 5 mol of hydrogen peroxide?
Conversions
• Problem Type 2
– Mole to mass
– Two conversion factors: mole
ratio & molar mass
• Given (mol) x mole ratio
(mol/mol) x molar mass
(g/mol) = unknown (g)
Conversions
• In photosynthesis, plants use
energy from the sun to produce
glucose C6H12O6, and oxygen
from the reaction of CO2 and
H2O. What mass, in grams, of
glucose is produced when 3.00
mol of H2O with CO2?
Conversions
• What mass of CO2, in grams, is
needed to react with 3.00 mol
of H2O in the photosynthetic
reaction described on the last
slide?
Conversions
• Problem Type 3
– Mass to moles
– Two conversion factors: molar
mass & mole ratio
• Given (g) x molar mass
(mol/g) x mole ratio
(mol/mol) = unknown (mol)
Conversions
• 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 of
NH3 and excess oxygen.
a.How many moles of NO are formed?
b.How many moles of H2O are
formed?
Conversions
• The compound PtCl2(NH3)2 is effective
as a treatment for some cancers. It is
synthesized by the reaction shown in
the following equation:
K2PtCl4 + 2NH3  2KCl + PtCl2(NH3)2
a.How many moles of K2PtCl4 must react
in order to produce 30.0 g of
PtCl2(NH3)2?
b.How many moles of NH3 are needed to
produce 30.0 g of PtCl2(NH3)2?
Conversions
• Problem Type 4
– Mass to mass
– Three conversion factors: molar
mass, mole ratio, molar mass
• Given (g) x molar mass
(mol/g) x mole ratio
(mol/mol) x molar mass
(g/mol) = unknown (g)
Conversions
• 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 + 2HF  SnF2 + H2
How many grams of SnF2 are
produced from the reaction of
30.00 g of HF with Sn?
Conversions
• Sodium peroxide reacts vigorously
with water to produce sodium
hydroxide and oxygen. The
unbalanced equation is the
following:
Na2O2 + H2O  NaOH + O2
a. What mass in grams of O2 is
produced when 50.0 g of Na2O2
react?
b. What mass in grams of water is
needed to react completely with
the Na2O2?
Limiting Reactants
• One reactant is present in
excess
• When one reactant is used up
reaction is over
• Limiting reactant
– Limits the production of product
• Excess reactant
– Not completely used up
Limiting Reactants
• C(s) + O2(g)  CO2(g)
– 5 mol C
– 10 mol O2
– More than enough O2 - 5 mol
excess
– Limiting - Carbon
Problem
• Silicon dioxide (quartz) is
usually quite unreactive but
reacts readily with hydrogen
fluoride according to the
following equation.
SiO2 + 4HF  SiF4 + 2H2O
If 2.0 mol of HF are exposed to
4.5 mol of SiO2, which is the
limiting reactant?
Problem
• The black oxide of iron, Fe3O4,
occurs in nature as the mineral
magnetite. This substance can
also be made in the laboratory
by the reaction between redhot iron and steam according
to the following equation.
3Fe + 4H2O  Fe3O4 + 4H2
Problem
3Fe + 4H2O  Fe3O4 + 4H2
a. When 36.0 g of H2O is mixed with
167 g of Fe, which is the limiting
reactant?
b. What mass in grams of black iron
oxide is produced?
c. What mass in grams of excess
reactant remains when the reaction
is completed?
Percent Yield
• Theoretical yield
– Maximum amount of product
• Actual yield
– Measured amount of product
produced
• Efficiency express in percent yield
% yield = (actual yield)/(theoretical yield) x 100
Problem
• Chlorobenzene, C6H5Cl, is used
in the production of many
important chemicals, such as
aspirin, and disinfectants. One
industrial method of preparing
chlorobenzene is to react
benzene, C6H6, with chlorine,
which is represented by the
following equation.
C6H6 + Cl2  C6H5Cl + HCl
• When 36.8 g of C6H6 react with
an excess of Cl2, the actual
yield of C6H5Cl is 38.8 g. What
is the percent yield of C6H5Cl?
Problem
• Huge quantities of sulfur
dioxide are produced from zinc
sulfide by means of the
following reaction.
2ZnS + 3O2  2ZnO + 2SO2
If the typical yield is 86.78%,
how much SO2 should be
expected if 4897 g of ZnS are
used
Chapter Review
• Pg. 295
– 8, 10, 11, 12, 14, 15, 22, 23, 24,
26, 28, 33