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 mass of 15 moles of copper?
Flashback:
What is the mass of 15 moles of copper?
How many moles is 500 g of copper?
What is the mass of 15 moles of Mg(OH)2?
How many moles is 500 g of Mg(OH)2?
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3. Balance: __Fe + __O2  __Fe2O3
Do Now:
Balance: __Fe + __O2  __Fe2O3
How many moles of Fe2O3 will form from 8 moles of Fe?
How many grams of Fe2O3 will form from 8 moles of Fe?
How many grams of Fe2O3 will form from grams of Fe?
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4. Writing and Using Mole Ratios
Moles Known
Moles Unknown
Using
Mole
Ratios
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5. 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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6. Writing and Using Mole Ratios
Mass-Mass Calculations
N2(g) + 3H2(g)  2NH3(g)
If I want to produce 150 grams of NH3, how many grams of hydrogen will I need?
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7. Calculating the Mass of a Product
Sample Problem 12.4
Calculating the Mass of a Product
Calculate the grams of NH3 produced when 5.40 g of H2 reacts with excess N2.
N2(g) + 3H2(g)  2NH3(g)
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8. Change given unit to moles
Sample Problem 12.4 
2 mol NH3
3 mol H2
5.40 g H2 
1 mol H2
2.0 g H2
17.0 g NH3
1 mol NH3
Given quantity
Change given unit to moles
Mole ratio
Change moles to grams
= 31 g NH3
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9. Phosphorus burns in air to produce tetraphosphorus decoxide:
4P(s) + 5O2(g)  P4O10(s)
What mass of phosphorus is needed to produce 3.25 mol of P4O10?
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10. Phosphorus burns in air to produce tetraphosphorus decoxide:
4P(s) + 5O2(g)  P4O10(s)
What mass of phosphorus is 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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11. How many grams of carbon dioxide is made when 100 grams of CH4 combusts with sufficient oxygen?
CH4 + 2O2  CO2 + 2H2O
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12. How many grams of carbon dioxide is 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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13. How many grams of Fe2O3 are produced when 12.0 grams of iron rusts?
Do Now
How many grams of Fe2O3 are produced when 12.0 grams of iron rusts?
4Fe + 3O2  2Fe2O3
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14. How many grams of Fe2O3 are produced when 12.0 grams of iron rusts?
Do Now
How many grams of Fe2O3 are produced when 12.0 grams of iron rusts?
4Fe + 3O2  2Fe2O3
159.8 g Fe2O3
1 mol Fe2O3
12.0 g Fe 
55.9 g Fe
1 mol Fe 
2 mol Fe2O3
4 mol Fe
= 17.2 g Fe2O3
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15. Other Stoichiometric Calculations
The mole can be related to other quantities:
1 mol = 6.02 x 1023 particles
1 mol of a gas = 22.4 L at STP
1 mol
6.02x1023 particles
and
1 mol
22.4 L
and
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16. Other Stoichiometric Calculations
The figure below summarizes the steps for a typical stoichiometric problem.
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17. 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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18. = 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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19. Volume-Volume Stoichiometric Calculations
Sample Problem 12.6
Volume-Volume Stoichiometric Calculations
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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20. 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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21. 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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22. 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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23. 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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24. 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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