1. Stoichiometry
Chapter 9

2. Big picture
Ch. 7 The mole
Ch.8 Balancing Chemical Equations
Ch.9 “Stoichiometry”
Target: How many grams of carbon dioxide are produced by burning 411 g of gasoline?

3. Notes
Stoichiometry
Theproportionalrelationshipbetweentwoormoresubstancesduringachemicalreaction.
The proportional relationship between two or more substances during a chemical reaction.

4. Real world stoichiometry problem
1 stick of butter + 3 eggs  2 cupcakes
1. If you have 60 eggs how many cupcakes can you make? (assuming you have unlimited butter)
2. How many eggs does it take to make 300 cupcakes?
1. ANS = 40 cupcakes
2. ANS = 450 eggs

5. 9.1 Practice: mole-to-mole conversion
C3H8 + 5O2  3CO2 + 4H2O
You have 4 mole of propane, (C3H8)
How many moles of O2 will it react with when it burns?
How many moles of CO2 form when it burns?
How many moles of H2O form when it burns?

6. 9.1 Practice: Mole-to-mole conversion
Given the following equation:
N2 + 3H2  2NH3
Calculate the number of moles of hydrogen needed to prepare 312 moles of ammonia.
See Graphic Organizer on p. 303

7. Notes Mole Ratio Used as conversion factor in stoichiometry problems.
x moles of unknown
y moles of given
x = coefficient of unknown in balanced chem eqn
y = coefficient of given in balanced chem eqn

8. 9.1 Mole to Mole conversions
Practice
P. 304
# 1a,b
# 2 a,b,c
P. 329
#21*,22,23
*h’wk

9. Mass-to-Mass conversion
See step-by-step procedure on p. 305 See graphic organizer on p. 306

10. Mass-to-Mass conversion
Typical Question
Imagine 7.5g of nitrogen gas (N2) reacts with excess* hydrogen gas per the following equation:
N2 + 3H2  2NH3
Calculate the mass of ammonia (NH3) produced
* Excess = “An amount or quantity beyond what is sufficient; a surplus.” = IGNORE!

11. Mass-to-Mass conversion
Imagine 7.5g of nitrogen gas (N2) reacts with excess hydrogen gas per the following equation:
N2 + 3H2  2NH3
Calculate the mass of ammonia (NH3) produced.
What is the ‘Given’ in the question?
What is the ‘Unknown’ in the question?
What is the molar mass of given and unknown?
What is the mole ratio that connects the Given and the Unknown?
ANSWER = 9.1 g

12. Stoichiometry calcs SUMMARY
WHEN IN DOUBT……TO BEGIN, CONVERT GIVEN TO MOLES
When one of the reactants is in excess  ignore it.

13. 9.1 Stoichiometry problems involving mass
What mass of NH3 can be made from 1221g of H2?
N2 + 3H2  2NH3
See Skills Toolkit 3 p. 306

14. 9.1 Stoichiometry Problems Involving Mass
Sample Problem B
(Follow along on P. 307)
What mass of NH3 can be made from 1221 g H2?
N2 + 3H2  2NH3

15. 9.1 Stoichiometry Problems Involving Mass
What mass of NH3 can be made from 1221g of H2?
N2 + 3H2  2NH3
GIVEN:
mass of H2 = 1221 g
molar mass of H2 = 2.02 g/mol
Mole ratio: 3 mol H2 = 2 mol NH3
UNKNOWN
mass of NH3 = ? g
( will need molar mass of NH3 = g/mol)

16. 9.1 Stoichiometry Problems Involving Mass
Step 1: To change grams to moles, use the molar mass of H2.
Step 2: The mole ratio must cancel out the units of mol H2 given in the problem and leave the units of mol NH3.
Therefore, the mole ratio is:
Step 3: To change moles of NH3 to grams, use the molar mass of NH3.

17. 9.1 Stoichiometry Problems Involving Mass

18. See page 305 for procedure 9.1 Problems Involving Mass
For Mass Calculations, Use Molar Mass
A mass-mass problem is a three-step process.
Step 1: Convert the given mass into moles.
Step 2: Use the mole ratio to convert moles of given to moles of unknown.
Step 3: Convert moles of known into grams.
See page 305 for procedure

19. Practice
Calculate the mass of hydrogen that would be needed to make 100 g of ammonia.

20. Practice: Stoichiometry Scratch paper
Calculate the mass of water formed from the combustion of 83 g of ethane C2H6
Balance the equation
GUESS
Write the 3 conversion factors will you need
ANS = 149 g

21. 9.1 Practice
p. 311 # 4 a,b How many grams of BrCl form when 212 g of Br2 react w/ excess Cl2?

22. 9.1 Stoichiometry Problems Involving Mass
Practice
See page 305 for procedure
P. 307 #1,2,3,4*
P. 330 # 24,25*,26**
* Show work to teacher when done
** Beast Mode

23. Next Generation Science Standard (NGSS)
HS-PS1-7. Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.
The Mole (Ch.7)
Balancing Equations (Ch.8)
Stoichiometry (Ch.9)

24. Combustion: CH4 + 2O2  CO2 + 2H2O
‘High Energy’ =
‘Reactive’ =
‘Unstable’
e.g. gasoline
Low Energy =
‘Unreactive’
‘Stable’
e.g. carbon dioxide

26. Photosynthesis

27. Global Warming

28. 9.1 Stoichiometry Problems Involving Mass
One gallon of gasoline (C8H18) weighs 2835 g. Calculate the mass of carbon dioxide produced by the combustion of one gallon of gasoline.
Follow along w/ Skills Toolkit p. 306
ANS = 8736 g

29. 9.1 Stoichiometry Problems Involving Mass
Gathering Information
Write the balanced chemical equation for the combustion of octane, C8H18
Calculate the molar mass of octane C8H18
Calculate the molar mass of carbon dioxide

30. Mass-Mass Stoich: Cellular Respiration
Calculate the number of grams of water that would theoretically be produced in cellular respiration by the combustion of 75.2 g of glucose.

31. Brainteaser
A bike shop has 10 bike frames and 16 wheels. How many complete bicycles can be assembled using these parts?
What would be left over?
8 complete bicycles.
2 frames left over.

32. Notes Limiting Reactant
Thesubstancethatcontrolsthequantityofproductthatcanforminachemicalreaction

33. Notes Limiting Reactant
The substance that controls the quantity of product that can form in a chemical reaction.
It runs out first 
Excess Reactant
Thesubstancethatisnotusedupcompletelyinachemicalreaction

34. Notes
Excess Reactant
The substance that is not used up completely in a chemical reaction.
Ignore it!
P. 313

35. Real world analogy: Limiting reagent
1egg + 3 spoonfuls of butter  2 cupcakes
If you have 9 eggs and 9 spoonfuls of butter, how many cupcakes can you make?
What ingredients would be left over? How much?
What ingredient would run out first?
6 cupcakes (theoretical yield)
6 eggs left over (eggs are in excess)
Butter is the ‘limiting reactant’.

36. 9.2 Limiting Reagent and Theoretical Yield
Practice: p. 331 # 33 p. 317 # 1,3,2