1
Chapter 5
Chemical Quantities and Reactions
5.1
The Mole
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2
Collection Terms
A collection termstates a specific number of items.
• 1 dozen donuts = 12 donuts
• 1 ream of paper = 500 sheets
• 1 case = 24 cans
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3
A moleis a collection that contains
• the same number of particles as there are carbon atoms in 12.0 g of carbon.
• 6.02 x 1023atoms of an element (Avogadro’s number).
1 mole element Number of Atoms 1 mole C = 6.02 x 1023C atoms 1 mole Na = 6.02 x 1023Na atoms 1 mole Au = 6.02 x 1023Au atoms
A Mole of Atoms
4 A mole• of a covalent compound has Avogadro’s number of molecules.
1 mole CO2= 6.02 x 1023CO2molecules 1 mole H2O = 6.02 x 1023H
2O molecules
• of an ionic compound contains Avogadro’s number of formula units.
1 mole NaCl = 6.02 x 1023NaCl formula units 1 mole K2SO4 = 6.02 x 1023K2SO4formula units
A Mole of a Compound
5
Samples of 1 Mole Quantities
1 mole of C atoms = 6.02 x 1023C atoms
1 mole of Al atoms = 6.02 x 1023Al atoms
1 mole of S atoms = 6.02 x 1023S atoms
1 mole of H2O molecules = 6.02 x 1023H
2O molecules
1 mole of CCl4 molecules = 6.02 x 1023CCl4molecules
6
Avogadro’s number, 6.02 x 1023, can be written as an
equality and two conversion factors.
Equality:
1 mole = 6.02 x 1023particles
Conversion Factors:
6.02 x 1023particles and 1 mole 1 mole 6.02 x 1023particles
Avogadro’s Number
Using Avogadro’s Number
Avogadro’s number is used to
o convert moles to particles
o convert particles to moles
7
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Converting Moles to Particles
Avogadro’s number is used to convert moles of a substance to particles.
How many Cu atoms are in 0.50 mole of Cu?
0.50 mole Cu x 6.02 x 1023Cu atoms
1 mole Cu
= 3.0 x 1023Cu atoms
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Converting Particles to Moles
Avogadro’s number is used to convert particles of a substance to moles.
How many moles of CO2are in
2.50 x 1024molecules CO 2? 2.50 x 1024molecules CO 2x 1 mole CO2 6.02 x 1023molecules CO 2 = 4.15 moles of CO2 10
1. The number of atoms in 2.0 mole of Al atoms is A. 2.0 Al atoms.
B. 3.0 x 1023 Al atoms.
C. 1.2 x 1024Al atoms.
2. The number of moles of S in 1.8 x 1024 atoms of S
is A. 1.0 mole of S atoms. B. 3.0 moles of S atoms. C. 1.1 x 1048moles of S atoms.
Learning Check
11Solution
C. 1.2 x 1024Al atoms 2.0 mole Al x 6.02 x 1023Al atoms = 1 mole Al B. 3.0 moles of S atoms 1.8 x 1024S atoms x 1 mole S = 6.02 x 1023S atoms 12Subscripts and Moles
The subscripts in a formulashow
• the relationship of atoms in the formula.
• the moles of each element in 1 mole of compound.
Glucose C6H12O6
In 1 molecule: 6 atoms C 12 atoms H 6 atoms O In 1 mole: 6 moles C 12 moles H 6 moles O
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Subscripts State Atoms and Moles
9 moles of C 8 moles of H 4 moles of O
14
Factors from Subscripts
The subscripts are used to write conversion factors for moles of each element in 1 mole of a compound. For aspirin, C9H8O4, the possible conversion factors are:
9 moles C 8 moles H 4 moles O 1 mole C9H8O4 1 mole C9H8O4 1 mole C9H8O4
and
1 mole C9H8O4 1 mole C9H8O4 1 mole C9H8O4
9 moles C 8 moles H 4 moles O
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Learning Check
A. How many moles of O are in 0.150 mole of aspirin, C9H8O4?
B. How many atoms of O are in 0.150 mole of aspirin, C9H8O4?
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Solution
A. Moles of O in 0.150 mole of aspirin, C9H8O4
0.150 mole C9H8O4 x 4 mole O = 0.600 mole of O
1 mole C9H8O4
subscript factor B. Atoms of O in 0.150 mole of aspirin, C9H8O4
0.150 mole C9H8O4 x 4 mole O x 6.02 x 1023O atoms
1 mole C9H8O4 1 mole O Avogadro’s number = 3.61 x 1023 atoms of O
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Chapter 5
Chemical Quantities and Reactions
5.2
Molar Mass
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Molar Mass
The molar mass
• is the mass of 1 mole of an element or compound.
• is the atomic or molecular mass expressed in grams.
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Molar Mass from Periodic Table
Molar mass is the atomic mass expressed in grams.
1 mole of Ag 1 mole of C 1 mole of S = 107.9 g = 12.01 g = 32.07 g
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Give the molar mass for each (to the tenths decimal place).
A. 1 mole of K atoms = ________
B. 1 mole of Sn atoms = ________
Learning Check
21
Give the molar mass for each (to the tenths decimal place).
A. 1 mole of K atoms = 39.1 g
B. 1 mole of Sn atoms = 118.7 g
Solution
Guide to Calculation Molar Mass of
a Compound
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Molar Mass of a Compound
The molar mass of a compound is the sum of the molar masses of the elements in the formula.
Example: Calculate the molar mass of CaCl2.
Element Number of Moles
Atomic Mass Total Mass
Ca 1 40.1 g/mole 40.1 g Cl 2 35.5 g/mole 71.0 g
CaCl2 111.1 g
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Molar Mass of K
3PO
4Calculate the molar mass of K3PO4.
Element Number of Moles
Atomic Mass Total Mass in K3PO4
K 3 39.1 g/mole 117.3 g P 1 31.0 g/mole 31.0 g O 4 16.0 g/mole 64.0 g
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Some 1-mole Quantities
32.1 g 55.9 g 58.5 g 294.2 g 342.2 g
One-Mole Quantities
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What is the molar mass of each of the following?
A. K2O
B. Al(OH)3
Learning Check
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A. K2O 94.2 g/mole
2 moles of K (39.1 g/mole) + 1 mole of O (16.0 g/mole) 78.2 g + 16.0 g = 94.2 g
B. Al(OH)378.0 g/mole
1 mole of Al (27.0 g/mole) + 3 moles of O (16.0 g/mole) + 3 moles of H (1.01 g/mole)
27.0 g + 48.0 g + 3.03 g = 78.0 g
Solution
28
Prozac, C17H18F3NO, is an antidepressant that inhibits
the uptake of serotonin by the brain. What is the molar mass of Prozac? 1) 40.1 g/mole 2) 262 g/mole 3) 309 g/mole
Learning Check
29Prozac, C17H18F3NO, is an antidepressant that inhibits the uptake of serotonin by the brain. What is the molar mass of Prozac? 3) 309 g/mole 17 C (12.0) + 18 H (1.01) + 3 F (19.0) + 1 N (14.0) + 1 O (16.0) = 204 g C + 18.2 g H + 57.0 g F + 14.0 g N + 16.0 g O = 309 g/mole
Solution
30Molar mass conversion factors
• are fractions (ratios) written from the molar mass.
• relate grams and moles of an element or compound.
• for methane, CH4, used in gas stoves and gas heaters
is
1 mole of CH4= 16.0 g (molar mass equality)
Conversion factors:
16.0 g CH4 and 1 mole CH4 1 mole CH4 16.0 g CH4
Molar Mass Factors
31
Acetic acid, C2H4O2, gives the sour taste to vinegar.
Write two molar mass conversion factors for acetic acid.
Learning Check
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32
Calculate molar mass for acetic acid C2H4O2:
24.0 g C + 4.04 g H + 32.0 g O = 60.0 g/mole C2H4O2 1 mole of acetic acid = 60.0 g acetic acid Molar mass factors:
1 mole acetic acid and 60.0 g acetic acid 60.0 g acetic acid 1 mole acetic acid
Solution
33
Molar mass factors are used to convert between the grams of a substance and the number of moles.
Calculations Using Molar Mass
Grams
Molar mass factor Moles34
Aluminum is often used to build lightweight bicycle frames. How many grams of Al are in 3.00 mole of Al?
Molar mass equality: 1 mole of Al = 27.0 g of Al
Setup with molar mass as a factor:
3.00 mole Al x 27.0 g Al = 81.0 g of Al 1 mole Al
molar mass factor for Al
Moles to Grams
35
Calculate the molar mass of C6H10S.
(6 x 12.0) + (10 x 1.01) + (1 x 32.1) = 114.2 g/mole
Set up the calculation using a mole factor. 225 g C6H10S x 1 mole C6H10S
114.2 g C6H10S
molar mass factor (inverted) = 1.97 moles of C6H10S
Solution
36
Grams, Moles, and Particles
37
Learning Check
How many H2O molecules are in 24.0 g of H2O?
1) 4.52 x 1023 H 2O molecules 2) 1.44 x 1025 H 2O molecules 3) 8.03 x 1023 H 2O molecules 38
Solution
How many H2O molecules are in 24.0 g of H2O?
3) 8.02 x 1023 24.0 g H2O x 1 mole H2O x 6.02 x 1023H2O molecules 18.0 g H2O 1 mole H2O = 8.03 x 1023H 2O molecules 39
Learning Check
If the odor of C6H10S can be detected from 2 x 10-13g
in 1 liter of air, how many molecules of C6H10S are
present?
40
Solution
If the odor of C6H10S can be detected from 2 x 10-13g
in 1 liter of air, how many molecules of C6H10S are
present? 2 x 10-13 g x 1 mole x 6.02 x 1023molecules 114.2 g 1 mole = 1 x 109molecules of C 6H10S are present 41
Solution
If the odor of C6H10S can be detected from 2 x 10-13g
in 1 liter of air, how many molecules of C6H10S are present? 2 x 10-13 g x 1 mole x 6.02 x 1023molecules 114.2 g 1 mole = 1 x 109molecules of C 6H10S are present 42
Chapter 5
Chemical Quantities and Reactions
5.3 Chemical Changes
43
Physical Change
In a physical change,• the state, shape, or size of the material changes.
• the identity and composition of the substance do not change.
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44
Chemical Change
In a chemical change,• reacting substances form new substances with different compositions and properties.
• a chemical reaction takes place.
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45
Some Examples of Chemical
and Physical Changes
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46
Classify each of the following as a 1) physical change or 2) chemical change.
A. ____Burning a candle. B. ____Ice melting on the street. C. ____Toasting a marshmallow. D. ____Cutting a pizza. E. ____Polishing a silver bowl.
Learning Check
47
Classify each of the following as a 1) physical change or 2) chemical change. A. 2 Burning a candle.
B. 1 Ice melting on the street. C. 2 Toasting a marshmallow. D. 1 Cutting a pizza. E. 2 Polishing a silver bowl.
Solution
48
Chemical Reaction
In a chemical reaction• a chemical change produces one or more new substances.
• there is a change in the composition of one or more substances.
49
Chemical Reaction
In a chemical reaction• old bonds are broken and new bonds are formed.
• atoms in the reactants are rearranged to form one or more different substances.
50
Chemical Reaction
In a chemical reaction• the reactants are Fe and O2.
• the new product Fe2O3 is
called rust.
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51
Chapter 5
Chemical Quantities and Reactions
5.4
Chemical Equations
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52
Chemical Equations
A chemical equationgives
• the formulas of the reactants on the left of the arrow.
• the formulas of the products on the right of the arrow.
Reactants Product
C(s)
O2(g) CO
2(g)
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Symbols Used in Equations
Symbolsin chemical equations show
• the states of the reactants.
• the states of the products.
• the reaction conditions.
TABLE
54
Chemical Equations are Balanced
In a balanced chemical reaction • no atoms are lost or gained. • the number of reacting atoms is equal to the number of product atoms.
55
A Balanced Chemical Equation
In a balanced chemical equation,
• the number of each type of atom on the reactant side is equal to the number of each type of atom on the product side.
• numbers called coefficientsare used in front of one or more formulas to balance the number of atoms.
Al + S Al2S3 Not Balanced
2Al + 3S Al2S3 Balanced using coefficients
2 Al = 2 Al Equal number of Al atoms 3 S = 3 S Equal number of S atoms
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A Study Tip: Using Coefficients
When balancing a chemical equation,
• use one or more coefficients to balance atoms.
• never change the subscripts of any formula.
N2 + O2 NO Not Balanced N2 + O2 N2O2 Incorrect formula N2 + O2 2NO Correctly balanced using coefficients 57
Learning Check
State the number of atoms of each element on the reactant side and the product side for each of the following balanced equations.
A. P4(s) + 6Br2(l) 4PBr3(g) B. 2Al(s) + Fe2O3(s) 2Fe(s) + Al2O3(s) 58
Solution
A. P4(s) + 6Br2(l) 4PBr3(g) 4 P atoms = 4 P atoms 12 Br atoms = 12 Br atoms B. 2Al(s) + Fe2O3(s) 2Fe(s) + Al2O3(s) 2 Al atoms = 2 Al atoms 2 Fe atoms = 2 Fe atoms 3 O atoms = 3 O atoms 59Learning Check
Determine if each equation is balanced or not. A. Na(s) + N2(g) Na3N(s)
B. C2H4(g) + H2O(l) C2H6O(l)
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Solution
Determine if each equation is balanced or not. A. Na(s) + N2(g) Na3N(s)
No. 2 N atoms on reactant side; only 1 N atom on the product side. 1 Na atom on reactant side; 3 Na atoms on the product side.
B. C2H4(g) + H2O(l) C2H6O(l)
Yes. 2 C atoms = 2 C atoms 6 H atoms = 6 H atoms 1 O atom = 1 O atom
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Guide to Balancing a Chemical
Equation
62
To balance the following equation,
Fe3O4(s) + H2(g) Fe(s) + H2O(l)
• work on one element at a time.
• use onlycoefficients in front of formulas.
• do not change any subscripts.
Fe: Fe3O4(s) + H2(g) 3Fe(s) + H2O(l)
O: Fe3O4(s) + H2(g) 3Fe(s) + 4H2O(l)
H: Fe3O4(s) + 4H2(g) 3Fe(s) + 4H2O(l)
Steps in Balancing an Equation
63
1. Write the equation with the correct formulas. NH3(g) + O2(g) NO(g) + H2O(g)
2. Determine if the equation is balanced. No, H atoms are not balanced. 3. Balance with coefficients in front of formulas.
2NH3(g) + O2(g) 2NO(g) + 3H2O(g)
Double the coefficients to give even number of O atoms. 4NH3(g) + 7O2(g) 4NO(g) + 6H2O(g)
Balancing Chemical Equations
64
4. Check that atoms of each element are equal in reactants and products.
4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g) 4 N (4 x 1 N) = 4 N (4 x 1 N) 12 H (4 x 3 H) = 12 H (6 x 2 H) 10 O (5 x 2 O) = 10 O (4 O + 6 O)
Balancing Chemical Equations
65
Equation for a Chemical Reaction
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66
Checking a Balanced Equation
Reactants Products 1 C atom = 1 C atom 4 H atoms = 4 H atoms 4 O atoms = 4 O atoms
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Check the balance of atoms in the following: Fe3O4(s) + 4H2(g) 3Fe(s) + 4H2O(l)
A. Number of H atoms in products. 1) 2 2) 4 3) 8 B. Number of O atoms in reactants.
1) 2 2) 4 3) 8 C. Number of Fe atoms in reactants.
1) 1 2) 3 3) 4
Learning Check
68
Fe3O4(s) + 4H2(g) 3Fe(s) + 4H2O(l)
A. Number of H atoms in products. 3) 8 (4H2O)
B. Number of O atoms in reactants. 2) 4 (Fe3O4)
C. Number of Fe atoms in reactants. 2) 3 (Fe3O4)
Solution
69
Balance each equation and list the coefficients in the balanced equation going from reactants to products: A. __Mg(s) + __N2(g) __Mg3N2(s) 1) 1, 3, 2 2) 3, 1, 2 3) 3, 1, 1 B. __Al(s) + __Cl2(g) __AlCl3(s) 1) 3, 3, 2 2) 1, 3, 1 3) 2, 3, 2
Learning Check
70 A. 3) 3, 1, 1 3Mg(s) + 1N2(g) 1Mg3N2(s) B. 3) 2, 3, 2 2Al(s) + 3Cl2(g) 2AlCl3(s)Solution
71Equations with Polyatomic Ions
2Na3PO4(aq) + 3MgCl2 (aq) Mg3( PO4(s) + 6NaCl(aq)
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Balancing with Polyatomic Ions
Na3PO4(aq) + MgCl2(aq) Mg3(PO4)2(s) + NaCl(aq)
Balance PO43-as a unit
2Na3PO4(aq) + MgCl2(aq) Mg3(PO4)2(s) + NaCl(aq) 2 PO43- = 2 PO
4
3-Check Na + balance
6 Na+ = 6 Na+
Balance Mg and Cl
2Na3PO4(aq) + 3MgCl2(aq) Mg3(PO4)2(s) + 6NaCl(aq)
3 Mg2+ = 3 Mg2+ 6 Cl- = 6 Cl
-73
Balance and list the coefficients from reactants to products. A. __Fe2O3(s) + __C(s) __Fe(s) + __CO2(g)
1) 2, 3, 2, 3 2) 2, 3, 4, 3 3) 1, 1, 2, 3
B. __Al(s) + __FeO(s) __Fe(s) + __Al2O3(s)
1) 2, 3, 3, 1 2) 2, 1, 1, 1 3) 3, 3, 3, 1
C. __Al(s) + __H2SO4(aq) __Al2(SO4)3(aq) + __H2(g)
1) 3, 2, 1, 2 2) 2, 3, 1, 3 3) 2, 3, 2, 3
Learning Check
74 A. 2) 2, 3, 4, 3 2Fe2O3(s) + 3C(s) 4Fe(s) + 3CO2(g) B. 1) 2, 3, 3, 12Al(s) + 3FeO(s) 3Fe(s) + 1Al2O3(s)
C. 2) 2, 3, 1, 3
2Al(s) + 3H2SO4(aq) 1Al2(SO4)3(aq) + 3H2(g)
Solution
75
Chapter 5
Chemical Quantities and Reactions
5.5
Types of Reactions
76
Type of Reactions
Chemical reactions can be classified as
• combination reactions.
• decomposition reactions.
• single replacement reactions.
• double replacement reactions.
77
Combination
In a combination reaction,
• two or more elements form one product.
• or simple compounds combine to form one product.
+ 2Mg(s) + O2(g) 2MgO(s) 2Na(s) + Cl2(g) 2NaCl(s) SO3(g) + H2O(l) H2SO4(aq) A B A B 78
Formation of MgO
79
Decomposition
In a decomposition reaction,
• one substance splits into two or more simpler substances.
2HgO(s) 2Hg(l) + O2(g)
2KClO3(s) 2KCl(s) + 3 O2(g)
80
Decomposition of HgO
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81
Learning Check
Classify the following reactions as 1) combination or 2) decomposition. ___A. H2(g) + Br2(g) 2HBr(l) ___B. Al2(CO3)3(s) Al2O3(s) + 3CO2(g) ___C. 4Al(s) + 3C(s) Al4C3(s) 82
Solution
Classify the following reactions as 1) combination or 2) decomposition. 1 A. H2(g) + Br2(g) 2HBr(l) 2 B. Al2(CO3)3(s) Al2O3(s) + 3CO2(g) 1 C. 4Al(s) + 3C(s) Al4C3(s) 83
Single Replacement
In a single replacementreaction,
• one element takes the place of a different element in another reacting compound.
Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g)
Fe(s) + CuSO4(aq) FeSO4(aq) + Cu(s)
84
Zn and HCl is a Single
Replacement Reaction
85
Double Replacement
In a double replacement,
• two elements in the reactants exchange places.
AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)
ZnS(s) + 2HCl(aq) ZnCl2(aq) + H2S(g)
86
Example of a Double
Replacement
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87
Learning Check
Classify the following reactions as
1) single replacement or 2) double replacement.
A. 2Al(s) + 3H2SO4(aq) Al2(SO4)3(s) + 3H2(g) B. Na2SO4(aq) + 2AgNO3(aq) Ag2SO4(s) + 2NaNO3(aq)
C. 3C(s) + Fe2O3(s) 2Fe(s) + 3CO(g)
88
Solution
Classify the following reactions as
1) single replacement or 2) double replacement. 1 A. 2Al(s) + 3H2SO4(aq) Al2(SO4)3(s) + 3H2(g)
2 B. Na2SO4(aq) + 2AgNO3(aq) Ag2SO4(s) + 2NaNO3(aq)
1 C. 3C(s) + Fe2O3(s) 2Fe(s) + 3CO(g)
89
Learning Check
Identify each reaction as 1) combination, 2) decomposition, 3) single replacement, or 4) double replacement.
A. 3Ba(s) + N2(g) Ba3N2(s)
B. 2Ag(s) + H2S(aq) Ag2S(s) + H2(g) C. SiO2(s) + 4HF(aq) SiF4(s) + 2H2O(l)
D. PbCl2(aq) + K2SO4(aq) 2KCl(aq) + PbSO4(s)
E. K2CO3(s) K2O(aq) + CO2(g)
90
Solution
1 A. 3Ba(s) + N2(g) Ba3N2(s)
3 B. 2Ag(s) + H2S(aq) Ag2S(s) + H2(g)
4 C. SiO2(s) + 4HF(aq) SiF4(s) + 2H2O(l)
4 D. PbCl2(aq) + K2SO4(aq) 2KCl(aq) +PbSO4(s)
91
Learning Check
Each of the following reactions occur in the formation of smog or acid rain. Identify the type of reaction and balance each. A. NO(g) + O2(g) NO2(s) B. N2(g) + O2(g) NO(g) C. SO2(g) + O2(g) SO3(g) D. NO2(g) NO(g) + O(g) 92
Solution
Each of the following reactions occur in the formation of smog or acid rain. Identify the type of reaction and balance each. Combination A. 2NO(g) + O2(g) 2NO2(s) B. N2(g) + O2(g) 2NO(g) C. 2SO2(g) + O2(g) 2SO3(g) Decomposition D. NO2(g) NO(g) + O(g) 93
Chapter 5
Chemical Quantities and Reactions
5.6
Oxidation-Reduction Reactions
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94
Oxidation and Reduction
An oxidation-reduction reaction
• provides us with energy from food.
• provides electrical energy in batteries.
• occurs when iron rusts.
4Fe(s) + 3O2(g) 2Fe2O3(s)
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95
An oxidation-reduction reaction involves
• a transfer of electrons from one reactant to another.
• oxidationas a loss of electrons (LEO).
• reduction as a gain of electrons (GER).
Electron Loss and Gain
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96
Oxidation and Reduction
97
Zn and Cu
2+Zn(s) Zn2+(aq) + 2e- oxidation
silver metal
Cu2+(aq) + 2e- Cu(s) reduction
blue solution orange
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98
Electron Transfer from Zn to Cu
2+Oxidation: loss of electrons
Reduction: gain of electrons
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99
Identify each of the following as 1) oxidation or 2) reduction. __A. Sn(s) Sn4+(aq) + 4e− __B. Fe3+(aq) + 1e− Fe2+(aq) __C. Cl2(g) + 2e− 2Cl-(aq)
Learning Check
100Identify each of the following as 1) oxidation or 2) reduction. 1 A. Sn(s) Sn4+(aq) + 4e− 2 B Fe3+(aq) + 1e− Fe2+(aq) 2 C. Cl2(g) + 2e− 2Cl-(aq)
Solution
101Write the separate oxidation and reduction reactions for the following equation.
2Cs(s) + F2(g) 2CsF(s)
A cesium atom loses an electron to form cesium ion. Cs(s) Cs+(s) + 1e− oxidation
Fluorine atoms gain electrons to form fluoride ions. F2(s) + 2e- 2F−(s) reduction
Writing Oxidation and Reduction
Reactions
102
In light-sensitive sunglasses, UV light initiates an oxidation-reduction reaction.
uv light
Ag+ + Cl− Ag + Cl
A. Which reactant is oxidized?
B. Which reactant is reduced?
103
Solution
In light-sensitive sunglasses, UV light initiates an oxidation-reduction reaction.
uv light
Ag+ + Cl− Ag + Cl
A. Which reactant is oxidized? Cl− Cl + 1e−
B. Which reactant is reduced? Ag+ + 1e− Ag
104
Learning Check
Identify the substances that are oxidized and reduced in each of the following reactions.
A. Mg(s) + 2H+(aq) Mg2+(aq) + H 2(g) B. 2Al(s) + 3Br2(g) 2AlBr3(s) 105
Solution
A. Mg is oxidized. Mg(s) Mg2+(aq) + 2e− H+is reduced. 2H+ + 2e− H 2 B. Al is oxidized. Al Al3+ + 3e− Br is reduced. Br + e− Br − 106Chapter 5
Chemical Quantities and Reactions
5.7
Mole Relationships in
Chemical Equations
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107
Law of Conservation of Mass
The
law of conservation of mass
indicates that in an
ordinary chemical reaction,
•
matter cannot be created or destroyed.
•
no change in total mass occurs in a
reaction.
•
mass of products is equal to mass of
reactants.
108
Conservation of Mass
2 moles of Ag + 1 mole of S = 1 mole of Ag2S
2 (107.9 g) + 1(32.1 g) = 1 (247.9 g) 247.9 g reactants = 247.9 g product
109
Consider the following equation:
4 Fe(s) + 3 O2(g) 2Fe2O3(s) This equation can be read in “moles” by placing
the
word “moles of” between each coefficient and formula.
4 moles of Fe + 3 moles ofO2 2 moles
of Fe2O3
Reading Equations in Moles
110
A mole-mole factoris a ratio of the moles for any two substances in an equation.
4Fe(s) + 3O2(g) 2Fe2O3(s)
Fe and O2 4 moles Fe and 3 moles O2
3 moles O2 4 moles Fe
Fe and Fe2O3 4 moles Fe and 2 moles Fe2O3
2 moles Fe2O3 4 moles Fe
O2and Fe2O3 3 moles O2 and 2 moles Fe2O3
2 moles Fe2O3 3 moles O2
Writing Mole-Mole Factors
111
Consider the following equation: 3H2(g) + N2(g) 2NH3(g)
A. A mole-mole factor for H2 and N2is
1) 3 moles N2 2) 1 mole N2 3) 1 mole N2
1 mole H2 3 moles H2 2 moles H2
B. A mole-mole factor for NH3and H2is
1) 1 mole H2 2) 2 moles NH3 3) 3 moles N2
2 moles NH3 3 moles H2 2 moles NH3
Learning Check
112
3H2(g) + N2(g) 2NH3(g) A. A mole-mole factor for H2 and N2is
2) 1 mole N2
3 moles H2
B. A mole-mole factor for NH3and H2is 2) 2 moles NH3
3 moles H2
Solution
113
How many moles of Fe2O3can form from 6.0 moles of O2?
4Fe(s) + 3O2(g) 2Fe2O3(s) Relationship: 3 mole O2 = 2 mole Fe2O3 Use a mole-mole factor to determine the moles of
Fe2O3.
6.0 mole O2 x 2 mole Fe2O3 = 4.0 moles of Fe2O3
3 mole O2
Calculations with Mole Factors
114
Guide to Using Mole Factors
115
How many moles of Fe are needed for
the reaction of 12.0 moles of O
2?
4Fe(s) + 3O
2(g) 2Fe
2O
3(s)
1) 3.00 moles of Fe
2) 9.00 moles of Fe
3) 16.0 moles of Fe
Learning Check
116In a problem, identify the compounds given and needed.
How many moles of Feare needed for the
reaction of 12.0 moles of O2?
4Fe(s) + 3O2(g) 2Fe2O3(s) The possible mole factors for the solution are
4 moles Fe and 3 moles O2
3 moles O2 4 moles Fe
Study Tip: Mole Factors
117
3) 16.0 moles of Fe
12.0
moles O
2x 4
moles Fe
=
16.0
moles of Fe
3
moles O
2Solution
118Chapter 5
Chemical Quantities and Reactions
5.8
Mass Calculations for Reactions
Copyright © 2009 by Pearson Education, Inc.
119
Moles to Grams
Suppose we want to determine the mass (g) of NH3 that can form from 2.50 moles of N2.
N2(g) + 3H2(g) 2NH3(g) The plan needed would be
moles N2 moles NH3 grams NH3
The factors needed would be:
mole factor NH3/N2and the molar mass NH3
120
Moles to Grams
The setup for the solution would be: 2.50 mole N2x 2 moles NH3 x 17.0 g NH3
1 mole N2 1 mole NH3
given mole-mole factor molar mass
121
How many grams of O2are needed to produce 0.400 mole of Fe2O3 in the following reaction?
4Fe(s) + 3O2(g) 2Fe2O3(s) 1) 38.4 g of O2 2) 19.2 g of O2 3) 1.90 g of O2
Learning Check
122Solution
2) 19.2 g of O2 0.400 mole Fe2O3x 3 mole O2 x 32.0 g O2= 19.2 g of O2 2 mole Fe2O3 1 mole O2mole factor molar mass
123
The reaction between H2and O2produces 13.1 g of water.
How many grams of O2reacted?
2 H2(g) + O2(g) 2 H2O(g) ? g 13.1 g The plan and factors would be
g H2O mole H2O mole O2 g of O2
molar mole-mole molar mass H2O factor mass O2
Calculating the Mass of a Reactant
124
Calculating the Mass of a Reactant
The setup would be:
13.1 g H2O x 1 mole H2O x 1 mole O2 x 32.0 g O2
18.0 g H2O 2 moles H2O 1 mole O2
molar mole-mole molar mass H2O factor mass O2
= 11.6 g of O2
125
Learning Check
Acetylene gas, C2H2, burns in the oxyacetylene torch for welding. How many grams of C2H2are burned if the reaction produces 75.0 g of CO2?
2C2H2(g) + 5O2(g) 4CO2(g) + 2H2O(g) 1) 88.6 g of C2H2 2) 44.3 g of C2H2 3) 22.2 g of C2H2 126
Solution
3) 22.2 g of C2H2 2C2H2(g) + 5O2(g) 4CO2(g) + 2H2O(g) 75.0 g CO2x 1 mole CO2 x 2 moles C2H2x 26.0 g C2H2 44.0 g CO2 4 moles CO2 1 mole C2H2molar mole-mole molar mass CO2 factor mass C2H2
127
Calculating the Mass of Product
When 18.6 g of ethane gas, C2H6, burns in oxygen, how
many grams of CO2are produced?
2C2H6(g) + 7O2(g) 4CO2(g) + 6H2O(g) 18.6 g ? g
The plan and factors would be
g C2H6 mole C2H6 mole CO2 g of CO2
molar mole-mole molar mass C2H6 factor mass CO2
128
Calculating the Mass of Product
2C2H6(g) + 7O2(g) 4CO2(g) + 6H2O(g)
The setup would be:
18.6 g C2H6x 1 mole C2H6x 4 moles CO2x 44.0 g CO2
30.1 g C2H6 2 moles C2H6 1 mole CO2
molar mole-mole molar mass C2H6 factor mass CO2
= 54.4 g of CO2
129
Study Tip: Check Units
Be sure to check that all units cancel to give the needed unit. Note each cancelled unit in the following setup:
needed unit g C2H6x mole C2H6 x moles CO2 x g CO2
g C2H6 moles C2H6 mole CO2
molar mole-mole molar mass C2H6 factor mass CO2
130
Learning Check
How many grams of H2O are produced when 35.8 g of
C3H8 react by the following equation?
C3H8(g) + 5O2(g) 3CO2(g) + 4H2O(g) 1) 14.6 g of H2O 2) 58.6 g of H2O 3) 117 g of H2O 131
Solution
2) 58.6 g of H2O C3H8(g) + 5O2(g) 3CO2(g) + 4H2O(g) 35.8 g C3H8x 1 mole C3H8 x 4 mole H2O x 18.0 g H2O 44.0 g C3H8 1 mole C3H8 1 mole H2Omolar mole-mole molar mass C3H8 factor mass H2O
= 58.6 g of H2O
132
Chapter 5
Chemical Quantities and Reactions
5.9
Energy in Chemical
Reactions
133
Collision Theory of Reactions
A chemical reaction occurs when
• collisions between molecules have sufficient energy to break the bonds in the reactants. • bonds between atoms of the reactants (N2
and O2) are broken and new bonds (NO) can
form.
Copyright © 2009 by Pearson Education, Inc.
134
Activation Energy
• The activation energy is the minimum energy needed for a reaction to take place.
• When a collision provides energy equal to or greater than the activation energy, product can form.
Copyright © 2009 by Pearson Education, Inc.
135
C(s) + 2H2(g) CH4(g) + 18 kcal
In an exothermic reaction,
• heat is released.
• the energy of the products is less than the energy of the reactants.
• heat is a product.
Exothermic Reactions
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136
Endothermic Reactions
In an endothermic
reaction
• Heat is absorbed.
• The energy of the
products is greater than the energy of the reactants.
• Heat is a reactant (added).
N2(g) + O2(g) + 43.3 kcal 2NO(g)
Copyright © 2009 by Pearson Education, Inc.
137
Learning Check
Identify each reaction as
1) exothermic or 2) endothermic.
A. N2 + 3H2 2NH3 + 22 kcal
B. CaCO3 + 133 kcal CaO + CO2
C. 2SO2 + O2 2SO3 + heat
138
Solution
Identify each reaction as
1) exothermic or 2) endothermic.
1 A. N2 + 3H2 2NH3 + 22 kcal
2 B. CaCO3 + 133 kcal CaO + CO2
139
Rate of Reaction
Reaction rate
• is the speed at which reactant is used up. • is the speed at which product forms.
• increases when temperature rises
because reacting molecules move faster, providing more colliding molecules with energy of activation.
140
Reaction Rate and Catalysts
A catalyst • increases the rate of a reaction. • lowers the energy of activation. • is not used up during the
reaction. Copyright © 2009 by Pearson Education, Inc.
141
Summary
Copyright © 2009 by Pearson Education, Inc.
142
Learning Check
State the effect of each on the rate of reaction as:
1) increases 2) decreases 3) no
change
A. increasing the temperature. B. removing some of the reactants. C. adding a catalyst.
D. placing the reaction flask in ice.
E. increasing the concentration of one of the reactants.
143
Solution
State the effect of each on the rate of reaction as:
1) increases 2) decreases 3) no change
1 A. increasing the temperature. 2 B. removing some of the reactants. 1 C. adding a catalyst.
2 D. placing the reaction flask in ice.
1 E. increasing the concentration of one of the reactants.
144
Learning Check
Indicate the effect of each factor listed on the rate of the
following reaction as:
1) increases 2) decreases 3) none
2CO(g) + O2(g) 2CO2 (g) A. raising the temperature
B. adding O2 C. adding a catalyst D. lowering the temperature
145
Solution
Indicate the effect of each factor listed on the rate of the
following reaction as
1) increases 2) decreases 3) none
2CO(g) + O2(g) 2CO2 (g) 1 A. raising the temperature 1 B. adding O2
1 C. adding a catalyst 2 D. lowering the temperature
146