Stoichiometry

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Stoichiometry is the part of chemistry that
studies amounts of substances that are involved
in reactions.
Stoichiometry
STOY-KEE-AHM-EH-TREE
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GOALS
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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
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Moles Molar Mass Review
Before we startlets review..
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• 1 mole is _______ atoms/molecules
• How many atoms are in 1.5 moles of neon?
• Calculate the number of grams in 3.25-mol of
  AgNO3
• How many moles are there in 250.0 grams of sodium
  phosphate (Na3PO4)?
• How many grams are in 5.6 x 1023 atoms of Zinc?

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Practice with a Friend ?
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1. What is the mass of 7.50 moles of sulfur dioxide
   (SO2)?
2. How many moles are there in 21.4 grams of
   nitrogen gas (N2)?
3. How many moles are there in 250.0 grams of sodium
   phosphate (Na3PO4)?
4. How many calcium atoms would be in a 100 gram
   sample of calcium
   metal?
5. Find the mass in grams of 7.5 ? 1015 atoms of
   nickel.

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amounts of substances that are involved in
reactions
Stoichiometry
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• Stoichiometry
• is the calculation of relative quantities of
  reactants and products in chemical reactions
• helps you figure out how much of a compound you
  will need, or maybe how much you started with.

2HCl Ba(OH)2 ? 2H2O BaCl2
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coefficients give MOLAR RATIOS
What are some molar ratio we can write from this
equation?
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Stoichiometry
amounts of substances that are involved in
reactions
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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
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Stoichiometry
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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?
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Stoichiometry
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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      1 atom  of S  ----gt   1
molecule of FeS                 10 atoms of Fe 
10 atoms of S ----gt 10 molecules of FeS 55.8
mg of Fe        32.1 mg S  ----gt   87.9 mg  FeS
5.58 g of Fe           3.21 g of S ----gt 8.79 g
of FeS
http//laude.cm.utexas.edu/courses/ch301/lecture/l
n2rf07.pdf
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Our goal..To be able to determine amounts of
products and reactantsmoles and grams.for ANY
chemical reaction.
2 CH3OH (l) 3 O2 (g) --gt 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

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Mole to Mole

• In the lab, you cant 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.

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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?
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Mole to Mole Practice
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• Carbon disulfide is an important industrial
  solvent. It is prepared by the reaction of
  carbon with sulfur dioxide
• 5C(s) 2SO2(g) ----gt CS2(s) 4CO(g)
• How many moles of CS2 form when 6.3 mol of C
  reacts?
• How many moles of carbon are needed to react
  with 7.24 moles of SO2?

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Mole to Mole Practice
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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?
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Mole to Mole Practice with a Friend
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• Use the following equation to answer the
  questions below
• 2 CH3OH (l) 3 O2 (g) --gt 2 CO2 (g) 4 H2O (l)
• How many moles of water will be produced from the
  combustion of 0.27 moles of CH3OH?
• How many moles of O2 are needed to burn 2.56
  moles of CH3OH?
• How many moles of CO2 are produced from the
  combustion of 5.25 moles of CH3OH?
• How many moles of water are produced when 3.25
  moles of CO2 are formed?

0.54 mol H2O
3.84 mol O2
5.25 mol CO2
6.50 mol H2O
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Mole to Mole Practice with a Friend
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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
8.6
moles NO2
6.How many moles of O2 can be produced from 4.3
moles of N2O5?
4.3 mol N2O5
moles O2
2.2
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Mass to Moles/ Moles to Mass
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2 KClO3 ---gt 2 KCl 3 O2

• 1.50 mol of KClO3 decomposes.
• How many grams of O2 will be produced?
• (1.50 mol of KClO3/1) x (3 O2/2 mol of KClO3) x
  (32g / 1 mol O2) 72 g

1.5 mol KCLO3
15.99g O2 1 Mol O2
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Mass to Moles/ Moles to Mass
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2 KClO3 ---gt 2 KCl 3 O2

• If 80.0 grams of O2 was produced, how many moles
  of KClO3 decomposed?
• We want to produce 2.75 mol of KCl. How many
  grams of KClO3 would be required?

337 g of KClO3
337 g of KClO3
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Practice with a friend
Mass to Moles/ Moles to Mass
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2 H2 O2 ---gt 2 H2O

• How many grams of H2O are produced when 2.50
  moles of oxygen are used?
• 2) If 3.00 moles of H2O are produced, how many
  grams of oxygen must be consumed?
• 3) How many moles of Li required to make 46.4 g
  of Li3N?

90 g of H2O
48 g of O2
6 Li(s) N2(g) ? 2 Li3N(s)
46.4 g Li3N x (1 mol Li3N/34.8 g Li3N) x (6 mol
Li/2 mol Li3N) 4.00 mol Li
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_Pb(NO3)2 _KI?_PbI2_KNO3
Mass to Moles/ Moles to Mass
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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?
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Mass to Moles/ Moles to Mass
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• 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
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Mass to Mass
Std Dev Mass-Mass conversions video clip
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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?
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Mass TO Mass
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• 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
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Mass to Mass Practice
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• How many grams of CO2 will be produced by the
  combustion of 15.0 g of propane?
• C3H8 (g) 5 O2 (g) --gt 3 CO2 (g) 4 H2O (l)
• How many grams of HCl are needed to react with
  27.62 g of Fe2O3?
• Fe2O3 (s) 6 HCl (g) --gt 2 FeCl3 (s) 3 H2O (g)

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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   -----gt  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
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Limiting Reactants
Download/Link Std Dev mod 7 limiting reactant
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• 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
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Limiting Reactants Calculations
How To 1-Calculate how much can be made by
both. The one with the least amount is the LR.
Example 1 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 limiting
reactant?
2H2 O2 ? 2H2O
Oxygen is limiting reactant, as the amount of H2O
is much less than that produced by hydrogen.
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http//www.lynden.wednet.edu/cms/lib02/WA01001013/
Centricity/Domain/93/Chemistry20Text/Limiting20R
eactant20Problems20text.pdf
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How To 1-Calculate how much can be made by
both. The one with the least amount is the LR.
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.
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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?
• 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?  

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Limiting Reactants -Practice with a friend
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Cu (s) 2AgNO3 (aq) ? Cu(NO3)2 (aq) 2Ag (s)
3) 5g of copper metal react with a solution
containing 20g of silver nitrate to produce
copper (II) nitrate and silver.
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.
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Reversible Reactions
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• 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 not-
• EX
• burning,
• combustion.

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Equilibrium
Std Dev Dynamic Equilibrium
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• At equilibrium, the concentration of all
  reactants and products stays constant.

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Dynamic Equilibrium
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• 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.
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Dynamic Equilibrium
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• 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.

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Factors Affecting Equilibrium
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• Le Chateliers Principle
• If stress is applied to a system in equilibrium,
  the system changes in a way that relieves the
  stress.
• Adding more reactant or product
• Change the temperature
• Change the Pressure

Le Chateliers Principle Video Clip
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(No Transcript)
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• Baking Soda Lab Video

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Reaction of Stoichiometry Calculations
Fe2O3 3CO ----gt 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?
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Fe2O3 3CO ----gt 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?