Stoichiometry

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1
Stoichiometry is the part of chemistry that studies
amounts of substances that are involved in reactions.
STOY-KEE-AHM-EH-TREE
2
GOALS
1. Demonstrate the conceptual
principle of limiting reactants.
2. Explain the role of
equilibrium in chemical
reactions
3. Identify and solve different types
of stoichiometry problems,
specifically relating mass to moles and
mass to mass.
The Mole Song- A Review
3
Before we start…let’s review…..
Moles & Molar Mass Review
• 1 mole is _______ atoms/molecules
• How many atoms are in 1.5 moles of neon?
1.5mol 6.02 x10 23 atoms
x
 9.0x10 23 atoms
1
1mol
• Calculate the number of grams in 3.25-mol of
 3
AgNO
• How many moles are there in 250.0 grams of
sodium phosphate (Na3PO4)? 250g x 1mol  1.52mol
• How many grams are in 5.6 x
Zinc?

1
164 g
1023 atoms
of
4
Practice with a Friend 
1. What is the mass of 7.50 moles of 7.5mol 64g
x
 480g
sulfur dioxide (SO2)?
1
1mol
2. How many moles are there in 21.4
21.4g 1mol
x
 0.764 mol
grams of nitrogen gas (N2)?
1
28g
3. How many moles are there in 250.0
250g 1mol
grams of sodium phosphate

x
 1.52mol
(Na3PO4)?
1
164 g
 be in
4. How many calcium atoms would
a 100 gram sample
100g 1m ol 6.02x1023 atom s
x
x
 1.5x1024 atom s
of calcium metal?
1
40g
1m ol
  1015
5. Find the mass in grams of 7.5
atoms of nickel.

5
Stoichiometry
Stoichiometry
“amounts of
substances that are
involved in reactions”
– is the calculation
2HCl + 1 Ba(OH)2  2H2O + 1 BaCl2
of relative
quantities of
reactants and
coefficients give MOLAR RATIOS
products in
chemical reactions
– helps you figure
out how much of a
What are some molar ratio we
can write from this equation?
compound you will
need, or maybe
how much you
started with.
6
Stoichiometry
“amounts of
substances that are
involved in reactions”
What do we know from this equation?
there is: one mole of CH4 for every two moles of H2O
there is: one mole of CH4 for every one mole of CO2
there are: 2 molecules of O2 for every one molecule
of CO2
there are even: four atoms of H in CH4 for every two
atoms of O in 2H2O
7
Stoichiometry
CH4 + 2O2  CO2 + 2H2O
there is: one mole of CH4 for every two moles of H2O
there are: 2 molecules of O2 for every one molecule of CO2
there are even: four atoms of H in CH4 for every two atoms of O in 2H2O
How can we write these as conversion factors?
Stoichiometry
8
Now you try: Write as many conversion factors as you can
1)
C3H8 + 5O2  3CO2 + 4H2O
What do we know from the balanced equation?
• 1 molecule of propane for every 3 molecules of CO2
• 3 atoms of C in propane for 4 molecules of water
• 9 atoms of hydrogen in propane for 8 atoms of hydrogen in water
2)
Fe + S  FeS
What do we know from the balanced equation?
1 atom of Fe
10 atoms of Fe
55.8 mg of Fe
5.58 g of Fe
+ 1 atom of S ----> 1 molecule of FeS
+ 10 atoms of S ----> 10 molecules of FeS
+
32.1 mg S ----> 87.9 mg FeS
+
3.21 g of S ----> 8.79 g of FeS
http://laude.cm.utexas.edu/courses/ch301/lecture/ln2rf07.pdf
Our goal..
To be able to determine amounts of
products and reactants…moles and
grams….for ANY chemical reaction.
2 CH3OH (l) + 3 O2 (g) --> 2 CO2 (g) + 4 H2O (l)
• Cutesy….but GOOD… video clip about
mole conversions.
• After this video, we will now have a
class rule about all conversions….
• You must go through………
• In the lab,
you can’t work
with single
atoms or
molecules. So,
it is useful to
be able to
identify how
many moles of
one substance
you need to
make a
certain
amount of
another
substance.
Mole to Mole
9
2KClO3 → 2KCl + 3O2
How many moles of oxygen are
produced by the decomposition of
6.0 moles of potassium chlorate?
N2 + 3H2 → 2NH3
How many moles of hydrogen are
needed to completely react with
2.0 moles of nitrogen?
Mole to Mole Practice
10
• Carbon disulfide is an important industrial solvent.
It is prepared by the reaction of carbon with
sulfur dioxide:
5C(s) + 2SO2(g) ----> CS2(s) + 4CO(g)
• How many moles of CS2 form when 6.3 mol of C
reacts? 6.3molC 1molCS 2
1
x
5molC
 1.26 molCS 2
• How many moles of carbon are needed to react
with 7.24 moles of SO2?
7.2m olSO2 5m olC
x
 18m olC
1
2m olSO2
Mole to Mole Practice
11
Silver can be made according to the following equation:
2AgNO3+ Ca Ca(NO3)2 + 2Ag
-If 35.3 moles of silver nitrate are reacted how many
moles of silver are produced?
5.3gAgNO3
2m olAg
x
 35.3m olAg
1
2m olAgNO3

Mole to Mole Practice with a Friend
12
Use the following equation to answer the questions below:
2 CH3OH (l) + 3 O2 (g) --> 2 CO2 (g) + 4 H2O (l)
1. How many moles of water will be produced from the combustion of
0.27 moles of CH3OH?
0.54 mol H2O
2. How many moles of O2 are needed to burn 2.56 moles of CH3OH?
3.84 mol O2
3. How many moles of CO2 are produced from the combustion of 5.25
moles of CH3OH? 5.25 mol CO
2
4. How many moles of water are produced when 3.25 moles of CO2 are
formed?
6.50 mol H2O
Mole to Mole Practice with a Friend
13
When N2O5 is heated, it decomposes:
2N2O5(g)

4NO2(g) + O2(g)
5. How many moles of NO2 can be produced from 4.3 moles of N2O5?
4.3 mol N2O5 4mol NO
2
2mol N 2O 5
=
8.6
moles NO2
6.How many moles of O2 can be produced from 4.3 moles of N2O5?
4.3 mol N2O5
1mol O 2
2mol N 2O 5
=
2.2
moles O2
Mass to Moles/ Moles to Mass
2 KClO3 ---> 2 KCl + 3 O2
• 1.50 mol of KClO3 decomposes.
– How many grams of O2 will be produced?
3mol O2
15.99g O2
1.5 mol KCLO3
2molKCLO3 1 Mol O2
• (1.50 mol of KClO3/1) x (3 O2/2 mol of
KClO3) x (32g / 1 mol O2) = 72
g
14
Mass to Moles/ Moles to Mass
15
2 KClO3 ---> 2 KCl + 3 O2
• If 80.0 grams of O2 was produced, how many
moles of KClO3 decomposed? 337 g of KClO
• We want to produce 2.75 mol of KCl. How
many grams of KClO3 would be required?
3
337 g of KClO3
16
Mass to Moles/ Moles to Mass
Practice with a friend
2 H2 + O2 ---> 2 H2O
1) How many grams of H2O are produced when
2.50 moles of oxygen are used?
90 g of H2O
2) If 3.00 moles of H2O are produced, how
many grams of oxygen must be consumed?
48 g of O2
6 Li(s) + N2(g)  2 Li3N(s)
3) How many moles of Li required to make 46.4 g
46.4 g Li N x (1 mol Li N/34.8 g Li N) x
of Li3N?
(6 mol Li/2 mol Li N) = 4.00 mol Li
3
3
3
3
Mass to Moles/ Moles to Mass
17
_Pb(NO3)2+ _KI_PbI2+_KNO3
4. How many grams of Pb(NO3)2 are needed to react completely with
9.00 mol KI?
1490g Pb(NO3)2
_CH4 + _O2  _CO2+_H2O
5. How many moles of water will be produced when 8.5 g of CH4 react
with oxygen?
0.81 mol O2
2N2O5(g)  4NO2(g) + O2(g)
6. How many moles of N2O5 were used if 210g of NO2 were produced?
Mass to Moles/ Moles to Mass
18
7. How many grams of chlorine are required to react completely
with 5.00 moles of sodium to produce sodium chloride?
2 Na +
Cl2  2 NaCl
8. Calculate the number of moles of ethane (C2H6) needed to
produce 10.0 g of water.
2 C2H6 + 7 O2  4 CO2 + 6 H20
19
Mass to Mass
Std Dev Mass-Mass
conversions video clip
MgCl2 (aq) + 2 AgNO3 (aq)  2 AgCl (s) + Mg(NO3)2 (aq)
How many grams of silver chloride could be produced by the
complete reaction of 19.7 g of magnesium chloride with silver
nitrate?
4 FeS2 + 11 O2 → 2 Fe2O3 + 8 SO2
If iron pyrite, FeS2, is not removed from coal, oxygen from
the air will combine with both the iron and the sulfur as coal
burns. If a furnace burns an amount of coal containing 125 g of
FeS2, how many grams of SO2 (an air pollutant) is produced?
20
Mass TO Mass
How many grams of water can I make from 25
grams of hydrogen gas and an excess of oxygen
gas, using the reaction
• 2 H2 + O2 2 H2O
225 grams of water
21
Mass to Mass Practice
1. How many grams of CO2 will be produced by the
combustion of 15.0 g of propane?
C3H8 (g) + 5 O2 (g) --> 3 CO2 (g) + 4 H2O (l)
2. How many grams of HCl are needed to react
with 27.62 g of Fe2O3?
Fe2O3 (s) + 6 HCl (g) --> 2 FeCl3 (s) + 3 H2O (g)
22
2N2O5(g)  4NO2(g) + O2(g)
3. How many grams of N2O5 are needed to produce 75.0
grams of O2?
4. Calculate how many grams of ammonia are produced
when you react 2.00g of nitrogen with excess hydrogen.
N2 + 3 H2  2 NH3
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2Al(s) + 6HCl(aq)  2AlCl3(aq)
+ 3H2(g)
5. How many grams of aluminum chloride can be produced
when 3.45 grams of aluminum are reacted with an excess
of hydrochloric acid?
2 C2H6
+ 7 O2 -----> 4 CO2 + 6 H2O
6. During its combustion, ethane C2H6, combines with
oxygen O2 to give carbon dioxide and water. A sample of
ethane was burned completely and the water that formed
has a mass of 1.61 grams. How many grams of ethane
was in the sample?
0.90 grams of ethane
24
Limiting Reactants
• Limiting Reactant - The
reactant in a chemical reaction
that limits the amount of
product that can be
formed. The reaction will stop
when all of the limiting reactant
is consumed.
Example: I want to assemble a gadget that
requires one nut, one bolt and two washers
for every hole. I have in my garage a bucket
filled with 12 washers, 4 bolts and five nuts.
What is the LIMITING SMALL METAL
OBJECT?
Goal: Demonstrate the
conceptual principle of
limiting reactants
Download/Link
Std Dev mod 7
limiting
reactant
Limiting Reactants Calculations
How To…
1-Calculate how
much can be made
Example 1:
by both.
You combine 10.0 grams of hydrogen gas and 15.0 grams of
oxygen gas. How many grams of water vapor are made? Which is The one with the
least amount is
the limiting reactant?
the LR.
2H2 + O2  2H2O
Oxygen is limiting reactant, as the amount of H2O is much less
than that produced by hydrogen.
25
http://www.lynden.wednet.edu/cms/lib02/WA01001013/Centricity/Domain/93/Chemistry%20Text/Limiting%20Reactant%20Problems
%20text.pdf
Limiting Reactants
Example 2:
If 5.00 grams of copper metal react with a solution containing
20.0 grams of AgNO3, which reactant is limiting and what mass
silver is produced? A copper (II) product is formed.
How To…
1-Calculate how
much can be made
by both.
The one with the
least amount is
the LR.
26
Limiting Reactants-Practice with a friend
1) 10.0g of aluminum reacts with 35.0 grams of chlorine gas to
produce aluminum chloride. Which reactant is limiting?
27
2 Al + 3 Cl2  2 AlCl3
CaO + 2HCl → CaCl2 + H2O
2)75 grams of calcium oxide react
with 130 grams of hydrochloric
acid to produce a salt and water.
What is the limiting reactant?
28
Limiting Reactants
-Practice with a friend
Cu (s) + 2AgNO3 (aq) → Cu(NO3)2 (aq) + 2Ag
3) 5g of copper metal react
with a solution containing 20g
of silver nitrate to produce
copper (II) nitrate and silver.
(s)
Al2S3 + 6 H2O → 2 Al(OH)3 + 3 H2S
4) 15.00 g of aluminum
sulfide and 10.00 g of
water react until the
limiting reagent is
consumed.
29
Reversible Reactions
A reversible reaction is one
in which the conversion of
reactants to products and
the conversion of products
to reactants occur
simultaneously.
Most reactions are
reversible. Some
are notEX:
burning,
combustion.
30
Equilibrium
Std Dev
Dynamic
Equilibrium
• At equilibrium, the concentration of all
reactants and products stays constant.
31
Dynamic Equilibrium
• It seems as if nothing is
happening, because the
macroscopic properties,
those you can see (e.g.
color and temperature),
do not change. However,
at the microscopic level
there is continual
change.
• No “NET” change
occurs.
• It is a DYNAMIC
STATE
Note: When the concentration of products stays
constant and the concentration of reactants stays
constant, the system is at equilibrium.
32
Dynamic Equilibrium
• Amounts are not
always 50/50 at
equilibrium.
• Depends on which one
is more favorable
(products or
reactants)
• Equilibrium refers
mainly to the RATE
of the reaction. Not
the amounts of
product and reactant.
33
Factors Affecting Equilibrium:
• Le Chatelier’s Principle
– If stress is applied to a
system in equilibrium, the
system changes in a way
that relieves the stress.
1. Adding more reactant
or product
2.Change the
temperature
3.Change the Pressure
Le Chatelier’s
Principle
Video Clip
34
35
36
Baking
Soda
Lab
Video
Reaction of Stoichiometry Calculations
Fe2O3 + 3CO ----> 2Fe + 3CO2
Questions we could ask about the reaction….
Question #1:
How many CO molecules are required to react with 25 formula units of Fe2O3?
Question #2.
How many Fe atoms are produced by reaction of 2.5 x 105 formula units of Fe2O3 with
excess CO?
Fe2O3 + 3CO ----> 2Fe + 3CO2
Question #3:
What mass of CO is required to react with 146 grams of Fe2O3?
Question #4:
What mass of CO2 can be produced by the reaction of 0.540 moles of Fe2O3?
…with excess CO?
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