1. Chapter 12 Stoichiometry 12.2 Chemical Calculations
12.1 The Arithmetic of Equations
12.2 Chemical Calculations
12.3 Limiting Reagent and
Percent Yield
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2. What is the mole ratio of Fe2O3 to Fe?
Do Now
4Fe + 3O2  2Fe2O3
What is the mole ratio of Fe2O3 to Fe?
What is the mole ratio of Fe2O3 to O2?
How many moles of Fe2O3 will form from 8 moles of Fe in excess oxygen?
If there are 127 moles of Fe, how many moles of Fe2O3 will form?
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3. Writing and Using Mole Ratios
Steps for Solving a Mass-Mass Problem
Grams Known
Moles Known
Moles Unknown
Grams Unknown
Using
Molar
Mass
Using
Mole
Ratios
Using
Molar
Mass
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4. What mass of phosphorus will be needed to produce 3.25 mol of P4O10?
Phosphorus burns in air to produce a phosphorus oxide in the following reaction:
4P(s) + 5O2(g)  P4O10(s)
What mass of phosphorus will be needed to produce 3.25 mol of P4O10?
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5. What mass of phosphorus will be needed to produce 3.25 mol of P4O10?
Phosphorus burns in air to produce a phosphorus oxide in the following reaction:
4P(s) + 5O2(g)  P4O10(s)
What mass of phosphorus will be needed to produce 3.25 mol of P4O10?
3.25 mol P4O10   = 403 g P
31.0 g P
1 mol P
1 mol P4O10
4 mol P
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6. How many grams of carbon dioxide will be made when 100 grams of CH4 combusts with sufficient oxygen?
CH4 + 2O2  CO2 + 2H2O
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7. How many grams of carbon dioxide will be made when 100 grams of CH4 combusts with sufficient oxygen?
CH4 + 2O2  CO2 + 2H2O
44 g CO2
1 mol CO2
100 g CH4 
16.0 g CH4
1 mol CH4 
= 275 g CO2
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8. Other Stoichiometric Calculations
The figure below summarizes the steps for a typical stoichiometric problem.
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9. Calculating the Molecules of a Product
Sample Problem 12.5
Calculating the Molecules of a Product
How many molecules of oxygen are produced when 29.2 g of water is decomposed by electrolysis according to this balanced equation?
2H2O(l) H2(g) + O2(g)
electricity
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10. = 4.88  1023 molecules O2 Sample Problem 12.5
1 mol O2 
2 mol H2O
29.2 g H2O 
1 mol H2O
18.0 g H2O
Given quantity
Change to moles
Mole ratio
Change to molecules
= 4.88  1023 molecules O2
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11. Volume-Volume Stoichiometric Calculations
Sample Problem 12.6
Volume-Volume Stoichiometric Calculations
Nitrogen monoxide and oxygen gas combine to form the brown gas nitrogen dioxide, which contributes to photochemical smog. How many liters of nitrogen dioxide are produced when 34 L of oxygen react with an excess of nitrogen monoxide? Assume conditions are at STP.
2NO(g) + O2(g)  2NO2(g)
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12. 34 L O2    1 mol O2 22.4 L O2 1 mol NO2 22.4 L NO2 2 mol NO2
Sample Problem 12.6
34 L O2   
1 mol O2
22.4 L O2
1 mol NO2
22.4 L NO2
2 mol NO2
Given quantity
Change to moles
Mole ratio
Change to liters
= 68 L NO2
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13. Finding the Volume of a Gas Needed for a Reaction
Sample Problem 12.7
Finding the Volume of a Gas Needed for a Reaction
Assuming STP, how many liters of oxygen are needed to produce 20.4 L SO3 according to this balanced equation?
2SO2(g) + O2(g)  2SO3(g)
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14. Finding the Volume of a Gas Needed for a Reaction
Sample Problem 12.7
Finding the Volume of a Gas Needed for a Reaction
Assuming STP, how many liters of oxygen are needed to produce 20.4 L SO3 according to this balanced equation?
2SO2(g) + O2(g)  2SO3(g)
10.2 L O2
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15. CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)
Methane burns in air by the following reaction:
CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)
What volume of water vapor is produced at STP by burning 501 g of methane?
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16. CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)
Methane burns in air by the following reaction:
CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)
What volume of water vapor is produced at STP by burning 501 g of methane?
22.4 L H2O
1 mol H2O
501 g CH4 
16.05 g CH4
1 mol CH4 
2 mol H2O
= 1.40  103 L H2O
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