Stoichiometry
Chapter 11
Skills from Previous Chapters
• The following skills are not the only ones, but
the main ones:
Name to formula
Balancing equations
Molar conversions
Conversion factors
Molar mass
New Skills to be Learned
Determine mole to mole ratios
Stoichiometric calculations
Mole to mole
Mole to gram
Gram to gram
Determine limiting reactant
What is stoichiometry?
• The study of quantitative relationships
between amounts of reactants used and
amounts of products formed by a chemical
reaction.
Mole to Mole Ratios
• First, we need an equation.
N2 + H 2 ® NH3
• Next we need to balance it.
2N2 + 3H 2 ® 2NH3
Mole to Mole Ratios
• Once, the equation is balanced, identify the
coefficients.
2N2 + 3H 2 ® 2NH3
• These coefficients form the basis of the ratios.
Mole to Mole Ratios
2N2 + 3H 2 ® 2NH3
• What is the ratio of hydrogen to nitrogen?
3molH 2
2molN 2
Problem 1
1. NaNO3 + PbO  Pb(NO3)2 + Na2O
• What is the mole ratio of PbO to Na2O?
• What is the mole ratio of NaNO3 to
Pb(NO3)2?
Problem 2
1. AgI + Fe2(CO3)3  FeI3 + Ag2CO3
• What is the mole ratio of AgI to FeI3?
• What is the mole ratio of Ag2CO3?
Problem 3
1. C2H4O2 + O2  CO2 + H2O
• What is the mole ratio of C2H4O2 to O2?
• What is the mole ratio of O2 to CO2?
Problem 4
1. ZnSO4 + Li2CO3  ZnCO3 + Li2SO4
• What is the mole ratio of ZnSO4 to ZnCO3?
• What is the mole ratio of Li2CO3 to ZnCO3?
Problem 5
1. V2O5 + CaS  CaO + V2S5
• What is the mole ratio of CaS to V2S5?
• What is the mole ratio of CaO to V2S5?
Mole to Mole Problems
• Mole to mole ratios are key in determining the
number of moles needed or produced of one
element or compound, when given the moles
of another.
Mole to Mole Problems
• First, an equation must be provided.
– Either in word or skeletal form.
• If in words, you must change it into skeletal.
H2 +O2 ®H2O
Mole to Mole Problems
• Second, the equation must be balanced.
2H2 +O2 ®2H2O
Mole to Mole Problems
• Third, read the problem carefully. Identify
what the problem is asking for.
• Example Problem:
– In the aforementioned reaction, if 12 moles of
hydrogen is reacted, how many moles of oxygen
would be needed to complete the reaction?
– What are they giving us?
• 12 moles of Hydrogen
– What are they looking for?
• Moles of oxygen
Mole to Mole Problems
• Once, the given and wanted are established,
we set up our problem. Since this is a mole to
mole problem, only ONE conversion factor is
needed.
molO2
wanted
12molH 2 ´
given ´
molH 2
given
Mole to Mole Problems
• In order to fill in the numbers, we must find
the mole ratio of hydrogen to oxygen. Then
we fill in the numbers.
2H2 +O2 ®2H2O
1molO2
12molH 2 ´
2molH 2
Mole to Mole Problems
• Lastly, we calculate the answer.
6molO2
Practice Problems
• C2H4O2 + O2  CO2 + H2O
• If Bob is reacting 20 moles of oxygen, how
many moles of carbon dioxide would he
produce?
• If Sue produced 12.5 moles of water, how
many moles of C2H4O2 were used?
Practice Problems (2)
• AgI + Fe2(CO3)3  FeI3 + Ag2CO3
• If .09 moles of Iron (III) iodide were produced,
how many of silver (I) carbonate were
produced?
• If 1.25 moles of iron (III) carbonate were used,
how many of silver (I) iodide should have
been?
Practice Problems (3)
• Al + O2  Al2O3
• If 30 moles of aluminum are used, how many
of aluminum oxide should be produced?
• If .05 moles of oxygen are used, how many of
aluminum oxide should be produced?
Homework
• P. 372
– Practice Problems 3 and 4
• P. 392
– #47 to 52
• Study for Quiz on Mole to Mole problems
Mole to Gram Problems
• Going from moles to grams in an equation is
based off of the ability to implement mole to
mole problems.
• Within these mole to gram problems, two
conversion factors will be used.
– Mole to mole ratios
– Molar mass
Mole to Gram Problems
• First, an equation must be provided.
– Either in word or skeletal form.
• If in words, you must change it into skeletal.
H2 +O2 ®H2O
Mole to Gram Problems
• Second, the equation must be balanced.
2H2 +O2 ®2H2O
Mole to Gram Problems
• Third, read the problem carefully. Identify
what the problem is asking for.
• Example Problem:
– In the aforementioned reaction, if 12 moles of
hydrogen is reacted, how many grams of oxygen
would be needed to complete the reaction?
– What are they giving us?
• 12 moles of Hydrogen
– What are they looking for?
• Grams of oxygen
Mole to Gram Problems
• Once, the given and wanted are established,
we set up our problem. Since this is a mole to
gram problem, two conversion factors are
needed.
middle wanted
given ´
´
given middle
Mole to Gram Problems
• In order to fill in the first conversion factor, we
must find the mole ratio of hydrogen to
oxygen. Then we fill in the numbers.
2H2 +O2 ®2H2O
1molO2
12molH 2 ´
2molH 2
Mole to Gram Problems
• In order to fill in the second conversion factor,
we must find the molar mass of O2.
1molO2 1molO2
=
(16 * 2)g
32g
Mole to Gram Problems
• Once, the given and wanted are established,
we set up our problem. Since this is a mole to
gram problem, two conversion factors are
needed.
1molO2
32g
12molH 2 ´
´
2molH 2 1molO2
Mole to Mole Problems
• Lastly, we calculate the answer.
192gO2
Practice Problems
• C2H4O2 + O2  CO2 + H2O
• If Bob is reacting 11 moles of oxygen, how
many grams of carbon dioxide would he
produce?
• If Sue produced 9 moles of water, how many
grams of C2H4O2 were used?
Practice Problems (2)
• AgI + Fe2(CO3)3  FeI3 + Ag2CO3
• If 9 moles of Iron (III) iodide were produced,
how many grams of silver (I) carbonate were
produced?
• If 1.5 moles of iron (III) carbonate were used,
how many grams of silver (I) iodide should
have been?
Practice Problems (3)
• Al + O2  Al2O3
• If 3 moles of aluminum are used, how many
grams of aluminum oxide should be
produced?
• If .5 moles of oxygen are used, how many
grams of aluminum oxide should be
produced?
Homework
• P. 376
– Practice problems # 13, 14
• Study for quiz
Gram to Gram Problems
• Going from grams to grams in an equation is
based off of the ability to implement mole to
mole problems.
• Within these mole to gram problems, three
conversion factors will be used.
– Molar mass
– Mole to mole ratios
– Molar mass
Gram to Gram Problems
• First, an equation must be provided.
– Either in word or skeletal form.
• If in words, you must change it into skeletal.
H2 +O2 ®H2O
Gram to Gram Problems
• Second, the equation must be balanced.
2H2 +O2 ®2H2O
Gram to Gram Problems
• Third, read the problem carefully. Identify
what the problem is asking for.
• Example Problem:
– In the aforementioned reaction, if 100g of
hydrogen is reacted, how many grams of oxygen
would be needed to complete the reaction?
– What are they giving us?
• 100g of Hydrogen
– What are they looking for?
• Grams of oxygen
Gram to Gram Problems
• Once, the given and wanted are established,
we set up our problem. Since this is a mole to
gram problem, three conversion factors are
needed.
mol mol g _ wanted
g _ given ´
´
´
g mol
mol
Gram to Gram Problems
• In order to fill in the first conversion factor, we
must find the molar mass of hydrogen. Then
we fill in the numbers.
1molH 2
12gH 2 ´
2g
Gram to Gram Problems
• In order to fill in the second conversion factor,
we must find the mole ratio of hydrogen to
oxygen.
2H2 +O2 ®2H2O
1molO2
1molH 2
Gram to Gram Problems
• To find the third conversion factor we must
find the molar mass of oxygen.
32g
1molO2
Mole to Mole Problems
• Lastly, we calculate the answer.
1molH 2 1molO2
32g
100gH 2 ´
´
´
= 880gO2
2g
2molH 2 1molO2
Practice Problems
• C2H4O2 + O2  CO2 + H2O
• If Bob is reacting 250 grams of oxygen, how
many grams of carbon dioxide would he
produce?
• If Sue produced 9 gramsof water, how many
grams of C2H4O2 were used?
Practice Problems (2)
• AgI + Fe2(CO3)3  FeI3 + Ag2CO3
• If 10 grams of Iron (III) iodide were produced,
how many grams of silver (I) carbonate were
produced?
• If 150grams of iron (III) carbonate were used,
how many grams of silver (I) iodide should
have been?
Practice Problems (3)
• Al + O2  Al2O3
• If 30 grams of aluminum are used, how many
grams of aluminum oxide should be
produced?
• If 500grams moles of oxygen are used, how
many grams of aluminum oxide should be
produced?
Homework
• P. 377
– Practice problems #15, 16
• Study for quiz
Limiting Reactants
limit the extent of the
reaction and, thereby, determines the amount
of product formed.
are the leftover reactants
when the reaction stops.
Limiting Reactant
• Involves Gram to Gram conversions
Example Problem
• The reaction between solid white phosphorus
(P4) and oxygen produces solid
tetraphosphorus decoxide (P4O10).
• Determine the mass of P4O10 formed if 25g of
P4 and 50g of oxygen are combined.
• How much excess reactant remains after the
reaction stops?
First
• Write the equation, and balance it.
P4 + 5O2 ® P4O10
Second
• Do gram to gram conversions for each of the
reactants.
1molP4 1molP4O10
284g
25gP4 ´
´
´
= 57.26gP4O10
124g
1molP4
1molP4O10
1molO10 1molP4O10
284g
50gO10 ´
´
´
= 44.38gP4O10
160g
2molO10 1molP4O10
So…
• The limiting reactant is the one that produces
the least amount!
• So, oxygen is the limiting reactant and 44.38g
of P4O10 are formed.
• Now, we must answer the second part of the
question.
Third
• Now, we must find out how much of the
excess reactant (P4) is left over. So we must
determine how much we use. To do this we
must back convert from the product to P4.
1molP4O10
1molP4
124g
44.38gP4O10 ´
´
´
=19.38gP4
284g
1molP4O10 1molP4
Fourth
• We subtract the used amount from the
original amount, and find the excess.
25g -
25g -19.38g = 5.62g
Problems
• Handouts
Homework
• P. 394
– #76 to 82
End of Chapter
• Time for review packet.