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Ch.12 notes with notations
1
March 06, 2018
Jan 167:57 AM
CHAPTER 12
Stoichiometry
May 2410:03 AM
12.1 Using Everyday Equations
• Stoichiometry is the calculation of quantities in chemical equations.
Feb 39:06 AM
3 eggs + 2 cups Flour + 1 Cup sugar 1 cake
* The balanced equation gives the ratios for the reactants and products.
• How many eggs are needed to make 4 cakes?
• How many cups of flour are needed if you wanted to use 9 eggs?
• If you needed to get rid of 5 cups of sugar, how many cakes must you make?
Feb 39:06 AM
Mg + 2HCl MgCl2 + H2
• How many moles of HCl are needed to react 2 moles of Mg?
• How many moles of H2 are produced if 6 moles of HCl reacts?
• How much Magnesium is needed to produce 7.6 moles of MgCl 2?
* The balanced equation gives the ratios for the reactants and products.* 1 mole of Mg reacts with 2 moles of HCl* 1 mole of MgCl 2 and 1 mole of H 2 are produced
May 2410:04 AM
Chemists use balanced chemical equations as a basis to calculate how much reactant is needed or product is formed in a reaction.
May 2410:04 AM
Interpreting Chemical Equations• N2(g) + 3H2(g) 2NH3(g)
• Rep. PARTICLES• MOLES• MASS • VOLUME
Ch.12 notes with notations
2
March 06, 2018
May 2410:04 AM
N2 + 3H2 2NH3 What is conserved in a Chemical Reaction?
Atoms Atoms
Mass Mass
Moles Moles
Molecules Molecules
Volume Volume
May 2410:04 AM
What is Conserved in Chemical Equations?
• Mass & atoms always!• Volume is not because temp. or
pressure can change.• Moles, molecules, and formula
units are not because atoms rearrange in a chemical reaction.
May 2410:04 AM
Ratios in chemical equations• What does excess mean?• If you have excess reagent, that
means you have plenty of it.
Reagent = Reactant
May 2410:05 AM
Ratios in chemical equations• Can change but should be listed in
lowest whole number form.• Lowest whole number Ratios are used
during mole to mole conversions.
Feb 39:06 AM
3 eggs + 2 cups Flour + 1 Cup sugar 1 cake
You have:> 12 eggs> 10 cups Flour> 8 cups sugar
Which ingredient limits the number of cakes you can bake?
Which ingredients do you have an excess of?
Feb 38:06 AM
Stoichiometric PathwaysN2(g) + 3H2(g) 2NH3(g)
How would you convert volume of nitrogen gas into mass of nitrogen trihydride?
Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g) How would you convert atoms of zinc into volume of hydrogen gas?
How would you convert moles of Zinc into formula units of zinc chloride?
Ch.12 notes with notations
3
March 06, 2018
Feb 117:10 AM
Comparing Atoms
Feb 117:10 AM
Comparing Molecules1 mol H2O 1 mol H2O2
6.02 x 1023 molecules 6.02 x 1023 moleculesH:O:
H:O:
gmm = 18g gmm = 34g
Feb 117:10 AM
Comparing Ionic Compounds1 mol CaCl2 1 mol Al2(CO3)3
6.02 x 1023 form units 6.02 x 1023 form units
Ca:Cl:
Al:C:O:
gfm = 111g gfm = 234g
May 2410:06 AM
12.2 CHEMICAL CALCULATIONS
• MoleMole Calculations• Begin with a mole quantity• End with a mole quantity• One step operation
Feb 69:00 AM
2KClO3 2KCl + 3O2
What mass of KCl is produced from 25.0g of KClO3?
25.0 grams KClO3
May 2410:06 AM
MoleMole Calculations
How many moles of ammonia can be produced from 0.60 mol of nitrogen gas?
N2(g) + 3H2(g) 2NH3(g)
Ch.12 notes with notations
4
March 06, 2018
May 2410:06 AM
More MoleMole Calculations4Al + 3O2 2Al2O3
How many moles of Al is needed to make 3.7 mol of Al2O3?
May 2410:06 AM
More MoleMole Calculations4Al + 3O2 2Al2O3
How many moles O2 is needed to completely react with 1.48 x 101 mol of Al?
May 2410:13 AM
More MoleMole Calculations
4Al + 3O2 2Al2O3
How many moles of Al2O3 can be made from 7.8 x 101 mol O2?
May 2410:13 AM
MassMass Calculations
4 step process• Mass• Change mass to moles• Mole mole ratio• Change mole to mass
May 2410:13 AM
More MassMass Calculations4Al + 3O2 2Al2O3
Grams of Al2O3 from 80.0 g of O2?
May 2410:13 AM
MassMass Calculations4Al + 3O2 2Al2O3
How many grams of Al is needed to form 4.56 x 106 grams of Al2O3 with an excess of oxygen?
Ch.12 notes with notations
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March 06, 2018
May 2410:13 AM
Other Stoichiometric Calculations
• Stoichiometry calculations may include any unit of measurement that is related to the mole.
• Molar Road Map
May 2410:13 AM
Molar Road MapMass
MOLVolume
Rep. Particles
Rep. Particles
Volume
Mass
May 2410:13 AM
Other Stoichiometric Calculations2H2O 2H2 + O2
How many molecules of oxygen are produced from 29.2 g of water?
May 2410:13 AM
2H2O 2H2 + O2
Assuming STP, how many liters of hydrogen are made from 4.32 x 1024 molecules of water?
May 2410:13 AM
N2 + 3H2 2NH3
Assuming STP, how many liters of ammonia are produced from 7.03 x 1025 molecules of hydrogen gas with an excess of nitrogen?
7.03 X 1025 molecules H2
May 2410:13 AM
4Al + 3O2 2Al2O3
Assuming STP, how many grams of aluminum are needed to produce 6.31 x 1031 formula units of Aluminum oxide with an excess of oxygen?
6.31 X 1031 Forms Al2O3
Ch.12 notes with notations
6
March 06, 2018
May 2410:13 AM
12.3 Limiting Reagent and Percent Yield
• Reactant that is used up first in a chemical reaction, or what you will run out of first.
• It determines the amount of product that can be formed.
May 2410:13 AM
EXCESS REAGENT
• Reactant that you have more than enough of.
• This will remain unchanged in the equation.
May 2410:13 AM
Example for UnderstandingYou are making omelet's...• Each omelet needs 3 eggs and 1 cup of cheese. • You have 12 eggs and 10 cups of cheese.
3 eggs + 1 cups cheese 1 omelet
• How many omelets can you make?
• Which ingredient limits the number of omelets you can make?
• Which ingredient will you have an excess of?
May 2410:13 AM
Determining Limiting Reagent• Using the amounts of substances present, perform a molmol conversion for each. This gives you the amount needed.
• Compare the amount needed with the amount present.
• Whichever substance has too little present is the limiting reagent.
* when given both reactants
May 2410:13 AM
Example #1: 2Na + Cl2 2NaCl
Given 6.70 mol of Na and 3.20 mol of Cl2.Step 1. What is the limiting reagent?
HAVE NEED
6.70 mol Na
3.20 mol Cl2
2 mol Na1 mol Cl2
1 mol Cl2
2 mol Na
Jan 299:53 AM
2Na + Cl2 2NaCl
Given 6.70 mol of Na and 3.20 mol of Cl2.Step 2: What is the excess reagent and how much excess is there?
Ch.12 notes with notations
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March 06, 2018
Jan 299:53 AM
2Na + Cl2 2NaCl
Given 6.70 mol of Na and 3.20 mol of Cl2.
Step 3. How many moles of NaCl are made?
3.20 mol Cl21 mol Cl2
2 mol NaCl
LR determines
Product made
Jan 299:49 AM
Example #2: 2Cu + S Cu2S
Given 80.0 g of copper and 25.0 g of sulfur.Step 1. What is the limiting reagent?
HAVE NEED
80.0 g Cu
25.0 g S
2 mol Cu1 mol S1 mol Cu
1 mol S
64 g Cu
32 g S 1 mol S2 mol Cu
1 mol S
1 mol Cu
32 g S
64 g Cu
Jan 299:49 AM
2Cu + S Cu2S
Given 80.0 g of copper and 25.0 g of sulfur.Step 2: What is the excess reagent and how much excess is there?
Jan 299:49 AM
2Cu + S Cu2SGiven 80.0 g of copper and 25.0 g of sulfur.Step 3. How much Cu 2S can be made?
80.0 g Cu2 mol Cu1 mol Cu2S1 mol Cu
64 g Cu 1 mol Cu2S160 g Cu2S
This answer should be in scientific notation...
Jan 299:49 AM
Example #3: N2 + 3H2 2NH3Given 341.0 L of N2 and 236.0 L of H2 @ STPStep 1. What is the limiting reagent?
Jan 299:49 AM
Step 2: What is the excess reagent and how much excess is there?
N2 + 3H2 2NH3
Given 341.0 L of N2 and 236.0 L of H2 @ STP
Ch.12 notes with notations
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March 06, 2018
Jan 299:48 AM
Step 3. How many grams of NH3 can be made?
N2 + 3H2 2NH3Given 341.0 L of N2 and 236.0 L of H2 @ STP
Jan 299:48 AM
N2 + 3H2 2NH3How many liters of NH3 are produced if 85.0grams of N2 and 85.0grams of H2 react @ STP?
Example #4:
May 2410:24 AM
Percent Yield• Theoretical yield: the maximum amount of product that can form from the amount of reactants given. > (Regular Stoichiometry)
• Actual yield: the amount of product that actually forms during a reaction. Cannot be greater than the theoretical yield. > (Often less)
• Percent yield: a percentage comparing the actual yield with the theoretical yield. (Same units)> % = (Actual ÷ Theoretical) x 100
Jan 168:48 AM
Determining Percent YieldCaCO3 CaO + CO2
24.8 g of calcium carbonate is heated to produce an actual yield of 13.1 g of calcium oxide.
1. What is the theoretical yield?
May 2410:25 AM
Determining Percent YieldCaCO3 CaO + CO2
24.8 g of calcium carbonate is heated to produce an actual yield of 13.1 g of calcium oxide.
2. What is the percent yield? (Must be same units!!)
Actual Yield
Theoretical Yieldx 100 =
Jan 168:43 AM
Determining Percent Yield2CuCl + H2S Cu2S + 2HCl
44.0 mol of CuCl forms an actual yield of 6.0 mol of Cu2S
1. Theoretical yield of Cu2S in moles?
Ch.12 notes with notations
9
March 06, 2018
May 2410:27 AM
2CuCl + H2S Cu2S + 2HCl
Actual Yield
Theoretical Yieldx 100 =
44.0 mol of CuCl forms an actual yield of 6.0 mol of Cu2S
3. What is the percent yield of Cu2S? (same units!)
May 2410:26 AM
4NH3 + 5O2 4NO + 6H2O
9.0 g of NH3 produces a percent yield of 63% water.
1. Theoretical yield of H2O in grams?2. Actual yield of H2O in grams?
Hint: Actual ÷ Theoretical = .63
Feb 137:40 AM
1. What is the theoretical yield of H2O in grams?
2. What is the actual yield of H2O (in grams) if only 63% was actually produced?
4NH3 + 5O2 4NO + 6H2O
Jan 168:48 AM
CaCO3 CaO + CO2
31.7 g of calcium carbonate is heated to produce an actual yield of 13.1 g of calcium oxide. What is the percent yield of CaO?
May 2410:13 AM
2Na + Cl2 2NaClGiven 4.50 mol of Na and 4.50 mol of Cl2, how many grams of NaCl can be produced?
HAVE NEED4.50 mol Na
4.50 mol Cl2
2 mol Na1 mol Cl2
1 mol Cl2
2 mol Na
Feb 287:27 AM