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CHAPTER 5 CHEM 101
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1
Chapter 5 Chemical Quantities and Reactions
5.1The Mole
Copyright © 2009 by Pearson Education, Inc.
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Collection Terms
A collection term statesa specific number of items.
• 1 dozen donuts = 12 donuts
• 1 ream of paper = 500 sheets
• 1 case = 24 cans
Copyright © 2009 by Pearson Education, Inc.
3
A mole is a collection that contains
• the same number of particles as there are carbon atoms in 12.0 g of carbon.
• 6.02 x 1023 atoms of an element (Avogadro’s number).
1 mole element Number of Atoms1 mole C = 6.02 x 1023 C atoms1 mole Na = 6.02 x 1023 Na atoms1 mole Au = 6.02 x 1023 Au atoms
A Mole of Atoms
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A mole • of a covalent compound has Avogadro’s number of
molecules.1 mole CO2 = 6.02 x 1023 CO2 molecules1 mole H2O = 6.02 x 1023 H2O molecules
• of an ionic compound contains Avogadro’s number of formula units.
1 mole NaCl = 6.02 x 1023 NaCl formula units1 mole K2SO4 = 6.02 x 1023 K2SO4 formula
units
A Mole of a Compound
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Samples of 1 Mole Quantities
1 mole of C atoms = 6.02 x 1023 C atoms
1 mole of Al atoms = 6.02 x 1023 Al atoms
1 mole of S atoms = 6.02 x 1023 S atoms
1 mole of H2O molecules = 6.02 x 1023 H2O molecules
1 mole of CCl4 molecules = 6.02 x 1023 CCl4 molecules
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Avogadro’s number, 6.02 x 1023, can be written as anequality and two conversion factors.
Equality:1 mole = 6.02 x 1023 particles
Conversion Factors:6.02 x 1023 particles and 1 mole
1 mole 6.02 x 1023 particles
Avogadro’s Number
Using Avogadro’s Number
Avogadro’s number is used to o convert moles to particleso convert particles to moles
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Converting Moles to Particles
Avogadro’s number is used to convertmoles of a substance to particles.
How many Cu atoms are in 0.50 mole of Cu?
0.50 mole Cu x 6.02 x 1023 Cu atoms1 mole Cu
= 3.0 x 1023 Cu atomsCopyright © 2009 by Pearson Education, Inc.
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Converting Particles to Moles
Avogadro’s number is used to convertparticles of a substance to moles.
How many moles of CO2 are in 2.50 x 1024 molecules CO2?
2.50 x 1024 molecules CO2 x 1 mole CO2
6.02 x 1023 molecules CO2
= 4.15 moles of CO2
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1. The number of atoms in 2.0 mole of Al atoms isA. 2.0 Al atoms.B. 3.0 x 1023 Al atoms.C. 1.2 x 1024 Al 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 1048 moles of S atoms.
Learning Check
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Solution
C. 1.2 x 1024 Al atoms2.0 mole Al x 6.02 x 1023 Al atoms =
1 mole Al
B. 3.0 moles of S atoms1.8 x 1024 S atoms x 1 mole S =
6.02 x 1023 S atoms
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Subscripts and Moles
The subscripts in a formula show• the relationship of atoms in the formula.• the moles of each element in 1 mole of compound.
GlucoseC6H12O6
In 1 molecule: 6 atoms C 12 atoms H 6 atoms OIn 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
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Factors from Subscripts
The subscripts are used to write conversion factors formoles of each element in 1 mole of a compound. Foraspirin, 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 C9H8O49 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 O1 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 1023 O atoms1 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
5.2Molar 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 massis 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 gCopyright © 2009 by Pearson Education, Inc.
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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
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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 gCl 2 35.5 g/mole 71.0 gCaCl2 111.1 g
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Molar Mass of K3PO4
Calculate the molar mass of K3PO4.
Element Number of Moles
Atomic Mass Total Mass in K3PO4
K 3 39.1 g/mole 117.3 gP 1 31.0 g/mole 31.0 gO 4 16.0 g/mole 64.0 gK3PO4 212.3 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)3 78.0 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
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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/mole2) 262 g/mole 3) 309 g/mole
Learning Check
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Prozac, C17H18F3NO, is an antidepressant that inhibits the uptake of serotonin by the brain. What is the molar mass of Prozac?
3) 309 g/mole17 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
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Molar 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
is1 mole of CH4 = 16.0 g (molar mass equality)
Conversion factors:16.0 g CH4 and 1 mole CH41 mole CH4 16.0 g CH4
Molar Mass Factors
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Acetic acid, C2H4O2, gives the sour taste to vinegar. Write two molar mass conversion factors for acetic acid.
Learning Check
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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
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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 Moles
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Aluminum is often used to build lightweight bicycleframes. 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 Al1 mole Al
molar mass factor for Al
Moles to Grams
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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 C6H10Smolar mass factor (inverted)
= 1.97 moles of C6H10S
Solution
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Grams, Moles, and Particles
A molar mass factor and Avogadro’s number convert…
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Learning Check
How many H2O molecules are in 24.0 g of H2O?
1) 4.52 x 1023 H2O molecules
2) 1.44 x 1025 H2O molecules
3) 8.03 x 1023 H2O molecules
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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 1023 H2O molecules 18.0 g H2O 1 mole H2O
= 8.03 x 1023 H2O molecules
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Learning Check
If the odor of C6H10S can be detected from 2 x 10-13 g in 1 liter of air, how many molecules of C6H10S are present?
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Solution
If the odor of C6H10S can be detected from 2 x 10-13 g in 1 liter of air, how many molecules of C6H10S are present?
2 x 10-13 g x 1 mole x 6.02 x 1023 molecules 114.2 g 1 mole
= 1 x 109 molecules of C6H10S are present
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Solution
If the odor of C6H10S can be detected from 2 x 10-13 g in 1 liter of air, how many molecules of C6H10S are present?
2 x 10-13 g x 1 mole x 6.02 x 1023 molecules 114.2 g 1 mole
= 1 x 109 molecules of C6H10S are present
42
Chapter 5 Chemical Quantities and Reactions
5.3 Chemical Changes
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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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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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Some Examples of Chemical and Physical Changes
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Classify each of the following as a1) 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
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Classify each of the following as a1) 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
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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.
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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.
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Chemical Reaction
In a chemical reaction
• the reactants are Fe and O2.
• the new product Fe2O3 is called rust.
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Chapter 5 Chemical Quantities and Reactions
5.4 Chemical Equations
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Chemical Equations
A chemical equation gives• 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) CO2 (g)
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Symbols Used in Equations
Symbols in chemical equations show
• the states of the reactants.
• the states of the products.
• the reaction conditions.
TABLE
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Chemical Equations are Balanced
In a balancedchemical reaction• no atoms are
lost or gained.
• the number of reacting atoms is equal to the number of product atoms.
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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 coefficients are used in front of one or more formulas to balance the number of atoms.
Al + S Al2S3 Not Balanced2Al + 3S Al2S3 Balanced using coefficients
2 Al = 2 Al Equal number of Al atoms3 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
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Learning Check
State the number of atoms of each element on thereactant side and the product side for each of thefollowing balanced equations.
A. P4(s) + 6Br2(l) 4PBr3(g)
B. 2Al(s) + Fe2O3(s) 2Fe(s) + Al2O3(s)
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Solution
A. P4(s) + 6Br2(l) 4PBr3(g)4 P atoms = 4 P atoms12 Br atoms = 12 Br atoms
B. 2Al(s) + Fe2O3(s) 2Fe(s) + Al2O3(s)2 Al atoms = 2 Al atoms2 Fe atoms = 2 Fe atoms3 O atoms = 3 O atoms
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Learning 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 atoms1 O atom = 1 O atom
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Guide to Balancing a Chemical Equation
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To balance the following equation, Fe3O4(s) + H2(g) Fe(s) + H2O(l)
• work on one element at a time.• use only coefficients 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
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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
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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
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Equation for a Chemical Reaction
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Checking a Balanced Equation
Reactants Products1 C atom = 1 C atom4 H atoms = 4 H atoms4 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
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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
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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
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A. 3) 3, 1, 13Mg(s) + 1N2(g) 1Mg3N2(s)
B. 3) 2, 3, 2 2Al(s) + 3Cl2(g) 2AlCl3(s)
Solution
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Equations 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 PO4
3- = 2 PO43-
Check Na + balance6 Na+ = 6 Na+
Balance Mg and Cl2Na3PO4(aq) + 3MgCl2(aq) Mg3(PO4)2(s) + 6NaCl(aq)
3 Mg2+ = 3 Mg2+
6 Cl- = 6 Cl-
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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
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A. 2) 2, 3, 4, 3 2Fe2O3(s) + 3C(s) 4Fe(s) + 3CO2(g)
B. 1) 2, 3, 3, 1 2Al(s) + 3FeO(s) 3Fe(s) + 1Al2O3(s)
C. 2) 2, 3, 1, 3 2Al(s) + 3H2SO4(aq) 1Al2(SO4)3(aq) + 3H2(g)
Solution
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Chapter 5 Chemical Quantities and Reactions
5.5Types of Reactions
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Type of Reactions
Chemical reactions can be classified as
• combination reactions.• decomposition reactions.• single replacement reactions.• double replacement reactions.
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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
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Formation of MgO
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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)
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Decomposition of HgO
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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)
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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)
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Single Replacement
In a single replacement reaction, • 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)
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Zn and HCl is a Single Replacement Reaction
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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)
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Example of a Double Replacement
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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)
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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)
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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)
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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)
2 E. K2CO3(s) K2O(aq) + CO2(g)
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Learning Check
Each of the following reactions occur in the formation of smog or acid rain. Identify the type of reaction andbalance 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)
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Solution
Each of the following reactions occur in the formation of smog or acid rain. Identify the type of reaction andbalance 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)
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Chapter 5 Chemical Quantities and Reactions
5.6Oxidation-Reduction Reactions
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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)Copyright © 2009 by Pearson Education, Inc.
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An oxidation-reduction reaction involves
• a transfer of electrons from one reactant to another.
• oxidation as a loss of electrons (LEO).
• reduction as a gain of electrons (GER).
Electron Loss and Gain
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Oxidation and Reduction
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97
Zn and Cu2+
Zn(s) Zn2+(aq) + 2e- oxidationsilver metal
Cu2+(aq) + 2e- Cu(s) reduction blue solution orange
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Electron Transfer from Zn to Cu2+
Oxidation: loss of electrons
Reduction: gain of electrons
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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
100
Identify 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
101
Write 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 initiatesan oxidation-reduction reaction.
uv lightAg+ + Cl− Ag + Cl
A. Which reactant is oxidized?
B. Which reactant is reduced?
Learning Check
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Solution
In light-sensitive sunglasses, UV light initiatesan oxidation-reduction reaction.
uv lightAg+ + Cl− Ag + Cl
A. Which reactant is oxidized? Cl− Cl + 1e−
B. Which reactant is reduced? Ag+ + 1e− Ag
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Learning Check
Identify the substances that are oxidized and reduced ineach of the following reactions.
A. Mg(s) + 2H+(aq) Mg2+(aq) + H2(g)
B. 2Al(s) + 3Br2(g) 2AlBr3(s)
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Solution
A. Mg is oxidized. Mg(s) Mg2+(aq) + 2e−
H+ is reduced. 2H+ + 2e− H2
B. Al is oxidized. Al Al3+ + 3e−Br is reduced. Br + e− Br −
106
Chapter 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 massindicates 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 Ag2S2 (107.9 g) + 1(32.1 g) = 1 (247.9 g)
247.9 g reactants = 247.9 g product
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109
Consider the following equation:4 Fe(s) + 3 O2(g) 2 Fe2O3(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 of O2 2 moles of Fe2O3
Reading Equations in Moles
110
A mole-mole factor is 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 O23 moles O2 4 moles Fe
Fe and Fe2O3 4 moles Fe and 2 moles Fe2O32 moles Fe2O3 4 moles Fe
O2 and 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 N2 is1) 3 moles N2 2) 1 mole N2 3) 1 mole N2
1 mole H2 3 moles H2 2 moles H2B. A mole-mole factor for NH3 and H2 is
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 N2 is2) 1 mole N2
3 moles H2
B. A mole-mole factor for NH3 and H2 is2) 2 moles NH3
3 moles H2
Solution
113
How many moles of Fe2O3 can 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
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115
How many moles of Fe are needed for the reaction of 12.0 moles of O2?4Fe(s) + 3O2(g) 2Fe2O3(s)
1) 3.00 moles of Fe 2) 9.00 moles of Fe3) 16.0 moles of Fe
Learning Check
116
In a problem, identify the compounds given and needed.
How many moles of Fe are 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 O23 moles O2 4 moles Fe
Study Tip: Mole Factors
117
3) 16.0 moles of Fe
12.0 moles O2 x 4 moles Fe = 16.0 moles of Fe
3 moles O2
Solution
118
Chapter 5 Chemical Quantities and Reactions
5.8Mass Calculations for Reactions
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119
Moles to Grams
Suppose we want to determine the mass (g) of NH3that 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/N2 and the molar mass NH3
120
Moles to Grams
The setup for the solution would be:
2.50 mole N2 x 2 moles NH3 x 17.0 g NH31 mole N2 1 mole NH3
given mole-mole factor molar mass
= 85.0 g of NH3
121
How many grams of O2 are 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 O23) 1.90 g of O2
Learning Check
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Solution
2) 19.2 g of O2
0.400 mole Fe2O3 x 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 H2 and O2 produces 13.1 g of water.How many grams of O2 reacted?
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 O2molar mole-mole molarmass H2O factor mass O2
Calculating the Mass of a Reactant
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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 O218.0 g H2O 2 moles H2O 1 mole O2molar mole-mole molarmass 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 C2H2 are burned if the reaction produces 75.0 g of CO2?
2C2H2(g) + 5O2(g) 4CO2(g) + 2H2O(g)
1) 88.6 g of C2H22) 44.3 g of C2H23) 22.2 g of C2H2
126
Solution
3) 22.2 g of C2H2
2C2H2(g) + 5O2(g) 4CO2(g) + 2H2O(g)
75.0 g CO2 x 1 mole CO2 x 2 moles C2H2 x 26.0 g C2H244.0 g CO2 4 moles CO2 1 mole C2H2
molar mole-mole molarmass CO2 factor mass C2H2
= 22.2 g of C2H2
127
Calculating the Mass of Product
When 18.6 g of ethane gas, C2H6, burns in oxygen, howmany grams of CO2 are 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 CO2molar mole-mole molarmass 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 C2H6 x 1 mole C2H6 x 4 moles CO2 x 44.0 g CO2
30.1 g C2H6 2 moles C2H6 1 mole CO2molar mole-mole molarmass 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 unitg C2H6 x mole C2H6 x moles CO2 x g CO2
g C2H6 moles C2H6 mole CO2
molar mole-mole molarmass 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 H2O2) 58.6 g of H2O3) 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 H2O44.0 g C3H8 1 mole C3H8 1 mole H2Omolar mole-mole molarmass C3H8 factor mass H2O
= 58.6 g of H2O
132
Chapter 5Chemical Quantities and Reactions
5.9 Energy in Chemical
Reactions
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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.
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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.
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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 endothermicreaction
• 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 kcalB. 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 kcal2 B. CaCO3 + 133 kcal CaO + CO2
1 C. 2SO2 + O2 2SO3 + heat
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
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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 temperatureB. adding O2C. adding a catalystD. lowering the temperature
145
Solution
Indicate the effect of each factor listed on the rate of the
following reaction as1) increases 2) decreases 3) none
2CO(g) + O2(g) 2CO2 (g)
1 A. raising the temperature1 B. adding O21 C. adding a catalyst2 D. lowering the temperature
146
Summary of Factors That Increase Reaction Rate
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