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 (in grams) of 5.4 moles of H2O?
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What is the mass (in grams) of 5.4 moles of H2O?
How many molecules of CH4 are in 6 moles of CH4?
How many moles of O2 molecules are in 44.8 L of O2 at STP?
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3. Writing and Using Mole Ratios
In chemical calculations, mole ratios are used to convert between a given number of moles of a reactant or product to moles of a different reactant or product.
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4. Combustion of Gasoline
Chemical Equations
Combustion of Gasoline
2C8H O2  16CO2 + 18H2O ∆H = -10,224 kJ
How many moles of CO2 will be produced from the combustion of 30 moles of C8H18?
(note: 30 moles C8H18 is ~ 1 gallon of gasoline)
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5. 2H2(g) + O2(g) ↔ 2H2O(l) ∆H = -482 kJ
Chemical Equations
Combustion of Hydrogen / Electrolysis
2H2(g) + O2(g) ↔ 2H2O(l) ∆H = -482 kJ
How many moles of O2 are required to react with 10 moles of H2?
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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. 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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8. Calculating the Mass of a Product
Sample Problem 12.4
Calculating the Mass of a Product
Calculate the number of grams of NH3 produced by the reaction of 5.40 g of hydrogen with an excess of nitrogen. The balanced equation is:
N2(g) + 3H2(g)  2NH3(g)
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9. 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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