Chapter 12 Notes
Honors Chemistry
Chapter 12: Stoichiometry
Section 1 Notes – The Arithmetic of Equations
(Read pages 353-358)
That’s the idea behind stoichiometry!!
 It’s like a _____________ ____________ for a _____________ _____________!
 It tells us how much _______________ is needed to _______________ a product.
 If a company wants to make _______________, they are going to make it in _______________.
So like _______________ the cake recipe, they just _______________ the _______________ of
a _______________.
Introduction to Stoichiometry
 A _______________ _______________ _______________ provides the same kind of
_______________ information that a _______________ does.
o How much _______________ you need to make something
Stoichiometry
 The _______________ of _______________ in ______________ _____________
 Use a _______________ _______________ _______________ to calculate how much
_______________ is needed or how much _______________ is formed in a chemical reaction
Remember our bike example from last chapter?
F + 2W + H + 2P  FW2HP2
Interpreting Chemical Equations
 A _______________ _______________ _______________ can be interpreted in terms of
different _______________; including number of _______________, ______________, or
______________; _______________, and ______________.
1
Chapter 12 Notes
Honors Chemistry
Interpret the following equation: N2 (g) +3 H2 (g)  2 NH3(g)
N2
+
3 H2

2 NH3
Atoms
Molecules
Moles
Particles
Mass
Volume
Mass Conservation in Chemical Reactions
 _______________ and _______________ are _______________ in every chemical reaction
Practice Problem
 Balance the following equation: ___C5H12 + ___O2  ___CO2 + ___H2O
 Interpret the above balanced equation in terms of:
o Atoms
o Moles
o Volumes of gas a STP
o Masses of reactants and products
Something Interesting to Consider
 Consider the reaction from the practice problem: ___C5H12 + ___O2  ___CO2 + ___H2O
 For every 1 mole of C5H12 that reacts, how many moles of O2 react as well? ________
 For every 1 mole of C5H12 that reacts, how many moles of CO2 will be produced? ________
 For every 1 mole of C5H12 that reacts, how many moles of H2O will be produced? ________
 What if 2 moles of C5H12 react? How many moles of O2, CO2, and H2O will be produced?
Book Work – Page 358 #5-10
2
Chapter 12 Notes
Honors Chemistry
Section 2 Notes – Chemical Calculations
(Read pages 359-366)
What is the most important unit for a chemist?
 The _______________!!
Next Step
 Now that you _______________ what a chemical _______________ tells us, we can
_______________ from _______________ of one _______________ to _______________ of
another _______________ using the _______________ from the _______________ in a
_______________.
 A ______________ _______________ is a _______________ _______________ derived from
the _______________ of a _______________ _______________ equation interpreted in terms
of _______________.
Example:
 How many moles of water can be produced when 5 moles of oxygen react with hydrogen?
o Step 1
 Need a _______________ _______________ _______________
 The _______________ is usually given to you – might not be
_______________!
o Step 2
 Think about what is _______________ and what is _______________
 Given moles of __________ and wants moles of __________
o Step 3
 What is the _______________ of _______________ in the equation?
o Step 4
 The mathematics - _______________!
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Chapter 12 Notes
Honors Chemistry
Practice Problems
11. This equation shows the formation of aluminum oxide, which is found on the surface of
aluminum objects exposed to the air: 4 Al + 3 O2  2 Al2O3. How many moles of aluminum are
needed to form 3.7 mol Al2O3?
12. According to the equation in Problem 11 (4 Al + 3 O2  2 Al2O3)
a. How many moles of oxygen are required to react completely with 14.8 moles of Al?
b. How many moles of Al2O3 are formed when 0.78 mol O2 react with aluminum?
One Step Further: General Mole Ratio Problem Solving Procedure
1. _______________ the given quantity to _______________
2. Use the _______________ _______________ from the _______________ equation to calculate
the number of _______________ of the _______________ substance
3. Convert the _______________ of _______________ _______________ to any other
_______________ measurement as directed by the _______________
a. 1 mole = ______________________________
b. 1 mole = ______________________________
c. 1 mole = ______________________________
You can only compare _______________ to _______________!!
Let’s Try It!
13. Acetylene gas (C2H2) is produced by adding water to calcium carbide (CaC2). Equation: CaC2 +
2 H2O  C2H2 + Ca(OH)2. How many grams of acetylene are produced by adding water to 5.00
g of CaC2?
a. Given: ______________________________
b. Want: ______________________________
c. Steps:
i. ______________________________
ii. ______________________________
iii. ______________________________
iv. ______________________________
4
Chapter 12 Notes
Honors Chemistry
Practice Problems
15. How many molecules of oxygen are produced by the decomposition of 6.54 g of potassium
chlorate (KClO3)? Equation: 2 KClO3  2 KCl + 3 O2.
16. The last step in the production of nitric acid is the reaction of nitrogen dioxide with water.
Equation: 3NO2 + H2O  2HNO3 + NO. How many grams of nitrogen dioxide must react with
water to produce 5.00 x 1022 molecules of nitrogen monoxide?
17. The equation for the combustion of carbon monoxide is 2 CO + O2  2 CO2. How many liters
of oxygen are required to burn 3.86 L of carbon monoxide?
18. Phosphorus and hydrogen can be combined to form phosphine (PH3).
Equation: P4 + 6 H2  4 PH3. How many liters of phosphine are formed when 0.42 L of
hydrogen reacts with phosphorous?
Additional Practice Problems
1. Rust is formed when iron reacts with oxygen. 4 Fe + 3 O2 → 2 Fe2O3
a. How many grams of Fe2O3 are produced when 12.0 g of iron rusts?
2. Hydrogen gas can be made by reacting methane (CH4) with high-temperature steam: CH4 +
H2O → CO + 3 H2
a. How many hydrogen molecules are produced when 158 g of methane reacts with steam?
3. Ammonia (NH3) reacts with oxygen to produce nitrogen monoxide and water. 4 NH3 + 5 O2
→ 4 NO + 6 H2O
a. How many liters of NO are produced when 1.40 L of oxygen reacts with ammonia?
Book Work – Page 366 #21 and 24
5
Chapter 12 Notes
Honors Chemistry
Section 3 Notes – Limiting Reagent and Percent Yield
(Read pages 368-375)
Back to the bike example
F + 2W + H + 2P  FW2HP2

If you were given the following items, how many bikes could you build?
o 51 frames
o 209 wheels
o 87 handlebars
o 132 pedals
In a chemical reaction, an _______________ ______________ of any _____________ will
_______________ the _______________ of _______________ that can form.
Try it in terms of a chemical reaction!

N2 + 3 H2  2 NH3
You have two moles of N2 and 3 moles of H2. How many moles of NH3 can you make?
Limiting and Excess Reactants
 _______________ Reactant
o _______________ that determines the amount of _______________ that can be
_______________ in a reaction
 _______________ Reactant
o _______________ that is not _______________ used up in the reaction. Does not
determine the _______________ of _______________ formed
 The amount of _______________ formed in a reaction can help determine the
_______________ _______________.
 A _______________ _______________ _______________ also helps determine the
_______________ reactant.
Determining the Limiting Reactant
1. Find the _______________ of each _______________.
2. Determine the _______________ _______________ of the _______________.
3. Use the _______________ of one _______________ to _______________ the
_______________ number of _______________ of the other _______________.
4. _______________ the number of _______________ of reactant _______________ to the
number of _______________ _______________ to determine the _______________ reactant.
a. Moles _______________ > Moles _______________ = _______________
b. Moles _______________ < Moles _______________ = _______________
6
Chapter 12 Notes
Honors Chemistry
Example
 Copper reacts with sulfur to form copper (I) sulfide according to the following balanced
equation. 2 Cu + S  Cu2S. What is the limiting reactant when 80.0g of Cu reacts with 25.0 g
of S?
o Step #1: Find the moles of each reactant.
o Step #2: Determine the mole ratio of the reactants.
o Step #3: Use the moles of one reactant to calculate the required number of moles of the
other reactant.
o Step #4: Compare the number of moles of reactant required to the number of moles
present to determine the limiting reactant.
Practice Problems
25. The equation for the complete combustion of ethane (C2H4) is:
C2H4 + 3 O2  2 CO2 + 2 H2O
If 2.70 mol of C2H4 is reacted with 6.30 mol O2, identify the limiting reactant.
26. Hydrogen gas can be produced by the reaction of magnesium metal with hydrochloric acid:
Mg + 2 HCl  MgCl2 + H2
Identify the limiting reactant when 6.00 g HCl reacts with 5.00 g Mg.
Make a note
 The _______________ present in the _______________ amount by _______________ or
_______________ is not necessarily the _______________ reactant.
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Chapter 12 Notes
Honors Chemistry
Determining the Quantity of Product Formed
 In order to determine how much _______________ will be formed in a reaction, use
_______________ _______________ to _______________ from the _______________ amount
of _______________ reactant to the _______________ of _______________.
Back to the previous example:
 Copper reacts with sulfur to form copper (I) sulfide according the following balanced equation.
2 Cu + S  Cu2S
 What is the maximum number of grams of Cu2S that can be formed when 80.0g of Cu reacts
with 25.0 g of S?
 Remember, we already calculated that Cu is the limiting reactant and S in in excess.
Practice Problems
27. The equation shows the incomplete combustion of ethane. C2H4 + 2 O2  2 CO + 2 H2O. If
2.70 moles of C2H4 is reacted with 6.30 mol O2
a. Identify the limiting reactant – Remember from practice problem #25, we determined that
C2H4 was the limiting reactant.
b. Calculate the number of moles of water produced.
28. The heat from an acetylene torch is produced by burning acetylene (C2H2) in oxygen. 2 C2H2 + 5
O2  4 CO2 + 2 H2O. How many grams of water can be produced by the reaction of 2.40 mol
C2H2 with 7.40 mol O2?
Introduction to Percent Yield
 You take a quiz in chemistry and receive an 18/20.
 What does a grade of 18/20 mean?
o _____________________________________________________________
o Your grade is an _______________ of how well you _______________
_______________ in _______________ to how well you _______________ have
_______________.
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Chapter 12 Notes
Honors Chemistry
Percent Yield
 A _______________ of the _______________ of a reaction
 Two parts:
o _______________ Yield
 The _______________ amount of _______________ that could be formed from a
_______________ amount of _______________.
 This would be the _______________ number of points on your test.
o _______________ Yield
 The amount of _______________ that _______________ forms when the
reaction is _______________ out.
 This would be the _______________ you _______________ on the test.
 Equation:
Ideal Percent Yield
 What should your ideal percent yield be? _______________
 Is it possible to have a percent yield greater or less than 100%? _______________
Variations in Percent Yield
 Percent yield _______________ than 100%
o _______________
o _______________ _______________
 Percent yield _______________ than 100%
o Reaction does _______________ go to _______________
o _______________
o _______________ _______________
o _______________ _______________ during _______________ or _______________
o _______________ _______________
Calculating Percent Yield
 _______________ yield is _______________. Use the _______________ reactant to determine
the amount of _______________ you should obtain.
 _______________ yield is _______________ or _______________ in an _______________.
9
Chapter 12 Notes
Honors Chemistry
Practice Problems
29. When 84.8 g of iron (III) oxide reacts with an excess of carbon monoxide, iron is produced:
Fe2O3 + 3 CO  2 Fe + 3 CO2. What is the theoretical yield of iron?
30. When 5.00 g of copper reacts with excess silver nitrate, silver metal and copper (II) nitrate are
produced. What is the theoretical yield of silver in this reaction?
Percent Yield Example
1. Calcium carbonate, which is found in seashells, is decomposed by heating. The balanced
chemical equation for the reaction is CaCO3 -----> CaO + CO2.
a. What is the theoretical yield of CaO when 24.8 g of CaCO3 is heated?
b. What is the percent yield of this reaction if 13.1 g of CaCO3 is produced?
Practice Problems
31. If 50.0 g of silicon dioxide is heated with an excess of carbon, 27.9 g of silicon carbide is
produced. SiO2 + 3 C  SiC + 2 CO. What is the percent yield of the reaction?
32. If 15.0 g of nitrogen reacts with 15.0 g of hydrogen, 10.5 g of ammonia (NH3) is produced.
What is the percent yield of the reaction?
Book Work – Page 375 #33-35
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