1. Created by C. Ippolito June 2007
Stoichiometry
12.1 The Arithmetic of Equations
12.2 Chemical Calculations
12.3 Limiting Reagent and Percent Yield
Updated 1/2/2019
Created by C. Ippolito June 2007

2. The Arithmetic of Equations
Objectives
Explain how balanced equations apply to both chemistry and everyday life
Interpret balanced equations in terms of moles, representative particles, mass, and gas volume at STP
Identify the quantities that are always conserved in chemical reactions
Updated 1/2/2019
Created by C. Ippolito June 2007

3. Using Everyday Equations
A balanced chemical equation provides the same kind of quantitative information that a recipe does
Tricycle Recipe
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Created by C. Ippolito June 2007 3

4. Using Balanced Chemical Equations
Chemists use balanced chemical equations as a basis to calculate how much reactant is needed or product is formed in a reaction
Stoichiometry
study of the calculation of quantities in chemical reactions
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Created by C. Ippolito June 2007 4

5. Using Balanced Equation as a Recipe
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Created by C. Ippolito June 2007 5

6. Interpreting Chemical Equations
A balanced equation can represent different quantities:
N2(g) + 3H2(g)  2NH3(g)
Atoms
reactants 2 atoms N & 6 atoms H
Molecules
ratio of molecules always 1:3:2
Moles
coefficients represent moles
Mass
if moles converted to grams
total # of grams of reactants = total # of grams of products
Volume
at STP convert moles to liters (1 mole = 22.4 L)
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Created by C. Ippolito June 2007 6

7. Mass Conservation in Chemical Reactions
Mass and atoms are conserved
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Created by C. Ippolito June 2007 7

8. Interpreting a Balanced Chemical Reaction
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Created by C. Ippolito June 2007 8

9. Chemical Calculations
Objectives
Construct mole ratios from balanced equations and apply these ratios in stoichiometric calculations
Calculate Stoichiometric quantities from balanced chemical equations using units of moles, mass, representative particles and volumes of gases at STP
Updated 1/2/2019
Created by C. Ippolito June 2007

10. Writing and Using Mole Ratios
conversion factor derived from coefficients
used to convert between
moles of reactant and moles of products
moles of reactants
moles of products
N2(g) + 3H2(g)  2NH3(g)
3 mole ratios in this equation
Updated 1/2/2019
Created by C. Ippolito June 2007 10

11. Mole-Mole Calculation
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Created by C. Ippolito June 2007 11

12. Mass-Mass Calculation
Steps to Solve Mass-Mass Problems
change given mass to moles
change moles of given to moles of wanted (unknown)
change moles of wanted to grams
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Created by C. Ippolito June 2007 12

13. Other Stoichiometric Calculations
In a typical problem:
given converted to moles
moles ratio used to calculate moles of unknown
moles of unknown converted to other unit of measurement
Updated 1/2/2019
Created by C. Ippolito June 2007 13

14. Stoichiometric Calculations
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Created by C. Ippolito June 2007 14

15. Calculating Molecules of Product
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Created by C. Ippolito June 2007 15

16. Volume-Volume Calculation
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Created by C. Ippolito June 2007 16

17. Finding Volume Needed for Reaction
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Created by C. Ippolito June 2007 17

18. Limiting Reagent and Percent Yield
Objectives
Identify the limiting reagent in a reaction
Calculate theoretical yield, actual yield, or percent yield given appropriate information
Updated 1/2/2019
Created by C. Ippolito June 2007

19. Limiting and Excess Reagents
An insufficient quantity of any of the reactants will limit the amount of product that forms
Limiting Reagent
reactant that determines the amount of product that can be formed in a reaction
Excess Reagent
reactant that is not completely used up in a reaction
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Created by C. Ippolito June 2007 19

20. Determining Limiting Reagent
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Created by C. Ippolito June 2007 20

21. Using Limiting Reagent to Find Quantity of Product
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Created by C. Ippolito June 2007 21

22. Created by C. Ippolito June 2007
Percent Yield
Theoretical Yield
maximum amount of product that could be produced from given amounts of reactants
Actual Yield
amount of product actually formed in the lab
Percent Yield
ratio of the actual yield to the theoretical yield expressed as a percent
Updated 1/2/2019
Created by C. Ippolito June 2007 22

23. Calculating Theoretical Yield
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Created by C. Ippolito June 2007 23

24. Calculating the Percent Yield
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Created by C. Ippolito June 2007 24