Unit 12 Stoichiometry
1
Stoichiometry
describing the
relative
quantities of
reactants,
products and
energy in a
chemical
reaction
http://visual.ly/chocolate-chip-cookies
Amedeo
Avogadro
?
quadrillions
thousands
trillions
billions
millions
1 mole = 602213673600000000000000
or 6.02 x 1023
How Big is a Mole?
One mole of marbles would cover the entire Earth
(oceans included) for a depth of two miles.
One mole of $1 bills stacked one on top
of another would reach from the Sun to
Pluto and back 7.5 million times.
It would take light 9500 years to travel from
the bottom to the top of a stack of 1 mole of $1 bill
Calculator tip
To enter 6.02 x 1023
Option 1: (6.02
2nd
Option 2: (6.02 x 10
,

23)
23)
The parentheses are important!
Practice: What is 6.02 x 1023 multiplied by 5?
Reminders
STAAR Chart
Remember Sig Figs!
Molar Mass
Al2O3 = 2(27.0) + 3(16.0) = 102.0 g/mol
Conversion
56.0 g Al2O3 = ? moles Al2O3
• 56.0 g Al2O3 x 1 mol Al2O3
102.0 g Al2O3
= 0.549
• Reminder: units should match and
then cancel on the diagonal!
• Calculator help: (56.0 x 1)  (102.0)
Mass, Volume, Mole Relationship
Mole Conversion Practice
1. A sample of carbon dioxide gas has a
volume of 75.9 liters.
How many moles of carbon dioxide gas
is this?
Mole Conversion Practice
2. You have a 4.26 mole sample of
magnesium nitrate.
How many grams does your sample
contain?
Mole Conversion Practice
3. You have a 7.56 mole sample of
sodium chloride.
Convert this to determine the number of
sodium chloride formula units (particles)
you have.
Mole Ratio
In a balanced chemical equation, the coefficients
describe the mole ratio.
2 H2 + 1O2  2 H2O
The mole ratios for this equation are:
2 mole H2: 1 mole O2
2 mole H2: 2 mole H2O
1 mole O2: 2 mole H2O
Balancing Equations Practice
1. Fe + S8  FeS
2. Na2O + H2O  NaOH
3. NH3 + O2  NO + H2O
Stoichiometry Island Diagram
Known
Unknown
Substance A
Substance B
M
Mass
Mass Mountain
Mass
Mole Island
Liter Lagoon
V
Volume
Mole
Mole
Volume
Particles
Particles
P
Particle Place
Stoichiometry Island Diagram
Stoichiometry Island Diagram
Mass
Volume
Known
Unknown
Substance A
Substance B
Mass
1 mole = 22.4 L @ STP
(gases)
Use coefficients
from balanced
Mole
Mole
chemical equation
1 mole = 22.4 L @ STP
Volume
(gases)
Particles
Particles
Stoichiometry Island Diagram
Practice 1: How many molecules of chlorine are
required to form 100. grams of sodium chloride?
Na + Cl2  NaCl + 441 kJ
1st: balance the equation
2nd: write the info from the word problem
above the equation
3rd: use mole island diagram to map out
your steps
4th: use dimensional analysis and mole ratios
to solve
1st: balance the equation
Na + Cl2  NaCl + 441 kJ
2nd: write the info from the word
problem above the equation
How many molecules of chlorine are required
to form 100.g sodium chloride?
?molecules
100.g
2 Na + Cl2  2 NaCl + 441 kJ
3rd: use mole island diagram to map out your steps
Stoichiometry Island Diagram
100. g
Mass
Known
Unknown
Substance A
Substance B
NaCl
1
Volume
1 mole = 22.4 L @ STP
Mass
Cl2
Use coefficients
from balanced
chemical equation
Mole
Mole
1 mole = 22.4 L @ STP
Volume
(gases)
(gases)
2
3
? molecules
Particles
Particles
Stoichiometry Island Diagram
4th: use dimensional analysis and mole
ratios to solve
?molecules
100.g
unknown
known
2 Na + Cl2  2 NaCl + 441 kJ
known
1
2
3
100.g NaCl x 1 mole NaCl x 1 mole Cl2 x (6.02 x 1023) molecules Cl2 =
58.5 g NaCl
2 mole NaCl
1 mole Cl2
Here’s how you set that up: (100 x 1 x 1 x 6.02 x 1023)  (58.5 x 2 x 1) =
How many grams of KClO3 are required to
produce 9.00 L of O2 at STP?
2KClO3  2KCl + 3O2
?g
9.00 L
9.00 L
O2
1 mol
O2
2 mol
KClO3
122.55
g KClO3
22.4 L
O2
3 mol
O2
1 mol
KClO3
x g KClO3 = 9.00 L O2
O2
1 mol O2
22.4 L O2
2 mol KClO3
3 mol O2
KClO3
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
122.55 g KClO3
1 mol KClO3
= 32.8 g
KClO3
32.8 g
= 32.8 g KClO3
How many grams of silver will be formed from
12.0 g copper?
Cu + 2 AgNO3  2 Ag + Cu(NO3)2
12.0 g
12.0
g Cu
?g
1 mol
Cu
63.55
g Cu
x g Ag = 12.0 g Cu
Cu
2 mol
Ag
1 mol
Cu
1 mol Cu
63.55 g Cu
107.87
g Ag
1 mol
Ag
2 mol Ag
1 mol Cu
Ag
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
107.87 g Ag
1 mol Ag
= 40.7 g
Ag
40.7 g
= 40.7 g Ag
Practice 2: How many grams of Na will be
needed to react with 10.L of Cl2 gas at STP?
2Na + Cl2  2NaCl + 441 kJ
Practice 2: How many grams of Na will be needed to react with 10.L of Cl2 gas at
STP?
2Na + Cl2  2NaCl + 441 kJ
Known
Mass
Volume
1 mole = 22.4 L @ STP
Substance A
Unknown
Substance B
Mass
Use coefficients
from balanced
chemical equation
Mole
Mole
1 mole = 22.4 L @ STP
Volume
(gases)
(gases)
Particles
Particles
Practice 3: Carbon reacts with sulfur dioxide to form carbon
disulfide and carbon monoxide in an exothermic reaction that
releases 160 kJ.
How many moles of CS2 form when
6.0 moles of C reacts with excess SO2?
Practice 3: Carbon reacts with sulfur dioxide to form
carbon disulfide and carbon monoxide in an exothermic
reaction that releases 160 kJ
How many grams of carbon are
needed to form 56.0 grams of CS2?
Actual and Theoretical Yields
• Theoretical Yield: calculated amount of
products
+
A
C

B
5g A + 5g B 
10g C
• Actual Yield: amount of product formed in
laboratory experiment
A
In a lab:
+
B

5g A + 5g B 
C
8g C
Calculating Percent Yield
• Percent Yield: indicates how much of
expected product was obtained in a reaction
Theoretical yield: 10 g Actual yield: 8g
( )
Percent yield = 8g (100) = 80% yield
10 g
Percent Yield Practice