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1
CHAPTER THREE
CHEMICAL EQUATIONS & REACTION CHEMICAL EQUATIONS & REACTION STOICHIOMETRYSTOICHIOMETRY
2
Chapter Three Goals
1.1. Chemical EquationsChemical Equations
2.2. Calculations Based on Chemical EquationsCalculations Based on Chemical Equations
3.3. Percent Yields from Chemical ReactionsPercent Yields from Chemical Reactions
4.4. The Limiting Reactant ConceptThe Limiting Reactant Concept
5.5. Concentrations of SolutionsConcentrations of Solutions
6.6. Dilution of solutionsDilution of solutions
7.7. Using Solutions in Chemical ReactionsUsing Solutions in Chemical Reactions
3
Chemical Equations
A chemical process is represented by a chemical equation
1. Reaction of methane with O2:
CH4 + 2O2 CO2 + 2H2O
reactantsreactants productsproducts
2. reactants on left side of reaction3. products on right side of equation4. relative amounts of each using stoichiometric coefficients
4
Chemical Equations
5
Chemical Equations
Look at the information an equation provides:
reactants yields products
1 formula unit 3 molecules 2 atoms 3 molecules
1 mole 3 moles 2 moles 3 moles
159.7 g 84.0 g 111.7 g 132 g
Fe O + 3 CO 2 Fe + 3 CO2 3 2
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Chemical Equations
Law of Conservation of Matter
– There is no detectable change in quantity of matter in
an ordinary chemical reaction.
– Balanced chemical equations must always include the
same number of each kind of atom on both sides of the
equation. Propane,C3H8, burns in oxygen to give carbon dioxide and water.
OH 4 CO 3 O 5 HC 22283
7
Law of Conservation of Matter
NH3 burns in oxygen to form NO & water
OH 6 + NO 4 O 5 + NH 4
correctlyor
OH 3 + NO 2 O + NH 2
223
2225
3
8
Law of Conservation of Matter
C7H16 burns in oxygen to form carbon dioxide and water. You do it! You do it!
Balancing equations is a skill acquired only with lots of practice– work many problems
OH 8 + CO 7 O 11 + HC 222167
9
Chemical Equations
Look at the information an equation provides:
reactants yields products
1 formula unit 3 molecules 2 atoms 3 molecules
1 mole 3 moles 2 moles 3 moles
159.7 g 84.0 g 111.7 g 132 g
Fe O + 3 CO 2 Fe + 3 CO2 3 2
10
Calculations Based on Chemical Equations
How many CO molecules are required to react with 25 formula units of Fe2O3?
CO of molecules 75
unit formula OFe 1
molecules CO 3OFe units formula 25 = molecules CO ?
3232
25 Fe2O3 + ? CO Product
1Fe2O3 needs 3 CO
25Fe2O3 needs ? CO
11
Calculations Based on Chemical Equations
How many iron atoms can be produced by the reaction of 2.50 x 105 formula units of iron (III) oxide with excess carbon monoxide?
atoms Fe 105.00 OFe units formula 1
atoms Fe 2
OFe units formula 102.50=atoms Fe ?
5
32
325
Fe2O3 + excess CO 2Fe + 3CO2 1Fe2O3 gives 2Fe
2.5 X 105 Fe2O3 gives ? Fe
12
Calculations Based on Chemical Equations
What mass of CO is required to react with 146 g of iron (III) oxide?
CO g 8.76CO mol 1
CO g 28.0
OFe mol 1
CO mol 3
OFe g 7.159
OFe mol 1OFe g 146 = CO g ?
3232
3232
Fe2O3 + 3CO Product
MW(Fe2O3) needs 3MW(CO)
146 g needs ?g CO
13
Calculations Based on Chemical Equations
What mass of carbon dioxide can be produced by the reaction of 0.540 mole of iron (III) oxide with excess carbon monoxide? Fe2O3 + excess CO 2Fe + 3CO2
1mol Fe2O3 gives 3 mol CO2
0.540 mol Fe2O3 gives ? mol CO2
? mol CO2 = ? g CO2/MW(g/mol) CO2
? g CO mol Fe O3 mol CO
1 mol Fe O
g CO
mol CO
= 71.3 g CO
2 2 32
2 3
2
2
2
0 54044 0
1.
.
14
Calculations Based on Chemical Equations
What mass of iron (III) oxide reacted with excess carbon monoxide if the carbon dioxide produced by the reaction had a mass of 8.65 grams? You do it!You do it!
Fe2O3 + excess CO 2Fe + 3CO2
? g Fe2O3 = 9.57 g Fe2O3
15
Percent Yields from Reactions
Theoretical yield is calculated by assuming that the reaction goes to completion.
Actual yield is the amount of a specified pure product made in a given reaction.
– In the laboratory, this is the amount of product that is formed in your beaker, after it is purified and dried.
Percent yield indicates how much of the product is obtained from a reaction.
% yield = actual yield
theoretical yield100%
16
Percent Yields from Reactions
A 10.0 g sample of ethanol, C2H5OH, was boiled with excess acetic acid, CH3COOH, to produce 14.8 g of ethyl acetate, CH3COOC2H5. What is the percent yield?
CH3COOH + C2H5OH CH3COOC2H5 + H2O
MW MW
10.0 g X (Theoretical Yield)
17
Percent Yields from Reactions
%5.77%100HCOOCCH g 19.1
HCOOCCH g 14.8= yield %
yield.percent theCalculate .2
HCOOCCH g 1.19
OHHC g 0.46
HCOOCCH g 88.0 OHHC g 10.0= HCOOCCH g ?
yield al theoretic theCalculate 1.
OH HCOOCCH OHHC + COOHCH
523
523
523
52
52352523
2523523
18
Percent Yields from Reactions
Salicylic acid reacts with acetic anhydride to form aspirin, acetylsalicylic acid. If the percent yield in this reaction is 78.5%, what mass of salicylic acid is required to produce 150. g aspirin?
2 C7H6O3 + C4H6O3 2 C9H8O4 + H2O salicylic acid acetic anhydride aspirin
29 billion tablets are consumedby Americans each year
MW = 138 g/mol MW = 180 g/mol
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Percent Yields from Reactions
2 C7H6O3 + C4H6O3 2 C9H8O4 + H2Osalicylic acid acetic anhydride aspirin
2MW 2MW X 191.08 (Theoretical Yield)
Answer: X = 146.5 g
actual Yield (150 g)
Theoretical Yield (g)78.5 = x 100
20
Limiting Reactant Concept
1. In a given reaction, there is not enough of one reagent to
use up the other reagents completely.
2. The reagent in short supply LIMITS the quantity of the
product that can be formed.
3. How many bikes can be made from 10 frames and 16 wheels?
1 frame + 2 wheels 1 bike
excess limiting
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Limiting Reactant Concept
22
Limiting Reactant Concept
When 100.0 g mercury is reacted with 100.0 g bromine to form mercuric bromide, which is the limiting reagent?
Hg + Br2 HgBr2
Thus the limiting reagent is
23
Limiting Reactant Concept
What is the maximum mass of sulfur dioxide that can be produced by the reaction of 95.6 g of carbon disulfide with 110. g of oxygen?
CS O CO 2 SO
1 mol 3 mol 1 mol 2 mol
76.2 g 3(32.0 g) 44.0 g 2(64.1 g)
2 2 2 2 3
24
Limiting Reactant Concept
22
2
2
2
2
222
22
2
2
2222
2222
SO g 147SO mol 1
SO g 1.64
O mol 3
SO mol 2
O g 32.0
O mol 1O g 110SO mol ?
SO g 161SO mol 1
SO g 1.64
CS mol 1
SO mol 2
g 76.2
CS mol 1CS g 6.95 SO mol ?
SO 2 CO O 3 CS
Which is limiting reactant? Limiting reactant is O2. What is maximum mass of sulfur dioxide? Maximum mass is 147 g.
25
Limiting Reactant Concept
If 25.0 g of each reactant were used in performing the
following reaction, which would be the limiting reactant?
(a) PbO2 (b) H2O (c) K2SO4 (d) PbSO4 (e) Cr2(SO4)3
3PbO2 + Cr2(SO4)3 + K2SO4 + H2O 3PbSO4 + K2Cr2O7 + H2SO4
If 20.0 g of each reactant were used in performing the
following reaction, which would be the limiting reactant?
(a) MnO2 (b) KOH (c) O2 (d) Cl2 (e) KMnO4
2MnO2 + 4KOH + O2 + Cl2 2KMnO4 + 2KCl + 2H2O
26
Concentration of Solutions
Definition of Solution: a homogeneous mixture of two or more substances dissolved in another.
A solution is composed of two parts:
(1) Solute: dissolved substance (or substance in the lesser amount).
(2) Solvent: dissolving substance (or substance in the greater amount).
– In aqueous solutions, the solvent is water.
Example: Solution of NaCl in water, H2O:
NaCl: solute, H2O: solvent
27
Concentration of Solutions
Concentration =Amount of solute
Mass or Volume of solutionRelative terms:Dilute solution: small amount of solute in large amount of solvent.Concentrated solution: large amount of solute in smaller amount of solvent (e.g. the amount of sugar in sweet tea can be defined by its concentration).We will discuss 2 concentration units:1- Percent by mass (do not confuse with % by mass of element in compound)2- Molarity
28
Concentration of Solutions
1- Percent by mass:
w/w% symbol thehas solute of massby %
solvent of mass + solute of mass =solution of mass
%100solution of mass
solute of mass = solute of massby %
Note: if the question says the solution is aqueous oe does notSpecify the solvent, the solvent is water, H2O.
29
Concentration of Solutions
Calculate the mass of potassium nitrate, KNO3 required to prepare 250.0 g of solution that is 20.0 % KNO3 by mass.
What is the mass of water in the solution?
(a) % by mass = g KNO3
g solutionx 100
20.0 % = g KNO3
250.0 gx 100
g KNO3 = 100
20.0 % x 250.0 g= 50.0 g
30
Concentration of Solutions
(b) mass of solution = mass of KNO3 + mass H2O
mass H2O = mass of solution - mass of KNO3
mass H2O = 250.0 g - 50.0 g
mass H2O = 200.0 g
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Concentration of Solutions
Calculate the mass of 8.00% w/w NaOH solution that contains 32.0 g of NaOH.
nsol' g .400
NaOH g 8.00
solution g 100.0NaOH g 32.0 =solution g ?
32
Concentration of Solutions
Calculate the mass of NaOH in 300.0 mL of an 8.00% w/w NaOH solution. Density is 1.09 g/mL.
You do it!You do it!
NaOH g 2.26nsol' g 100
NaOH g 8.00
nsol' mL 1
nsol' g 1.09nsol' mL 300.0 = NaOH g ?
33
Concentrations of Solutions
What volume of 12.0% KOH contains 40.0 g of KOH? The density of the solution is 1.11 g/mL.
You do it!You do it!
solution mL .300
solution g 1.11
solution mL 1
KOH g 12.0
solution g 100.0KOH g 40.0 =solution mL ?
34
Concentrations of Solutions
2- Second common unit of concentration: Molarity
35
Concentrations of Solutions
2- Second common unit of concentration: Molarity
mL
mmolL
molessolution of liters ofnumber
solute of moles ofnumber molarity
M
M
36
Concentrations of Solutions
Calculate the molarity of a solution that contains 12.5 g of sulfuric acid in 1.75 L of solution.
You do it!You do it!
42
42
42
424242
SOH 0728.0L
SOH mol 0728.0
SOH g 98.1
SOH mol 1
nsol' L 75.1
SOH g 12.5
nsol' L
SOH mol ?
M
37
Concentrations of Solutions
Determine the mass of calcium nitrate required to prepare 3.50 L of 0.800 M Ca(NO3)2 .
You do it!You do it!
? g Ca(NO L 0.800 mol Ca(NO
L164 g Ca(NO
mol Ca(NO g Ca(NO
33
3
33
) .)
)
))
22
2
22
3 50
1459
38
Concentrations of Solutions
One of the reasons that molarity is commonly used is because:
M x L = moles solute
and
M x mL = mmol solute
39
Concentrations of Solutions
The specific gravity of concentrated HCl is 1.185 and it is 36.31% w/w HCl. What is its molarity?
HCl 11.80HCl g 36.46
HCl mol 1
nsol' g 100
HCl g 31.36
solution L
solution g 1185 = HCl/L mol ?
1185g/Lor g/mL 1.185=density
us tells1.185 =gravity specific
M
40
Dilution of Solutions
To dilute a solution, add solvent to a concentrated
solution.
– One method to make tea “less sweet.”
The number of moles of solute (before and after
dilution) in the two solutions remains constant.
The relationship M1V1 = M2V2 is appropriate for dilutions,
but not for chemical reactions.
41
Dilution of Solutions
Common method to dilute a solution involves the use of volumetric flask, pipet, and suction bulb.
42
Dilution of Solutions
Take-Home Calculations (M x V)A = (M x V)B
M x V = moles of solute M x V = W/MW (M x V)A = (W/MW)A
OR (M x V)A = (W/MW)B
W = M x V x MW
43
Dilution of Solutions
If 10.0 mL of 12.0 M HCl is added to enough water to give 100. mL of solution, what is the concentration of the solution?
M
MM
MM
MM
20.1mL 100.0
mL 0.100.12
mL 100.0mL 0.10 0.12
VV
2
2
2211
44
Dilution of Solutions
What volume of 18.0 M sulfuric acid is required to make 2.50 L of a 2.40 M sulfuric acid solution?
You do it!You do it!
mL 333or L 0.333 18.0
2.40 L 2.50V
V V
V V
1
1
221
2211
M
M
M
M
MM
45
Using Solutions in Chemical Reactions
Combine the concepts of molarity and stoichiometry to determine the amounts of reactants and products involved in reactions in solution.
46
Using Solutions in Chemical Reactions
What volume of 0.500 M BaCl2 is required to completely react with 4.32 g of Na2SO4?
L 0.0608 BaCl mol 0.500
BaCl L 1
SONa mol 1
BaCl mol 1
SONa g 142
SONa mol 1 SOgNa 4.32 BaCl L ?
NaCl 2 + BaSO BaCl + SONa
2
2
42
2
42
42422
4242
47
Using Solutions in Chemical Reactions
(a)What volume of 0.200 M NaOH will react with 50.0 mL 0f 0.200 M aluminum nitrate, Al(NO3)3?
You do it!
3333 NaNO 3OHAlNaOH 3NOAl
48
Using Solutions in Chemical Reactions
(a) What volume of 0.200 M NaOH will react with 50.0 mL 0f 0.200 M aluminum nitrate?
nsol' NaOH mL 150or L 0.150 NaOH mol 0.200
NaOH L 1
)Al(NO mol 1
NaOH mol 3
nsol' )Al(NO L 1
n sol' )Al(NO mol 0.200mL 1000
L 1nsol' )Al(NO mL 50.0 = NaOH mL ?
NaNO 3Al(OH)NaOH 3NOAl
3333
33
33
3333
49
Using Solutions in Chemical Reactions
(b) What mass of Al(OH)3 precipitates in (a)?
3
3
3
33
3
33
33
333
Al(OH) g 780.0
Al(OH) mol 1
Al(OH) g 0.78
)Al(NO mol 1
Al(OH) mol 1
nsol' )Al(NO L1
)Al(NO mol 0.200mL 1000
L1nsol' )Al(NO mL 50.0 Al(OH) g ?
50
Homework AssignmentHomework Assignment
One-line Web Learning (OWL):One-line Web Learning (OWL):
Chapter 3 Exercises and Tutors – Chapter 3 Exercises and Tutors – OptionalOptional
51
End of Chapter 3