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Chapter 5 Chemical Reactions and Quantities 5.3

Types 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 (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) + 3O2(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

a 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 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 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 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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Chapter 5 Chemical Reactions and Quantities

5.4 Oxidation-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)

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An oxidation-reduction reaction §  Transfers electrons from one reactant to another.

A Loss of Electrons is Oxidation (LEO) Zn(s) Zn2+(aq) + 2e-

A Gain of Electrons is Reduction (GER) Cu2+(aq) + 2e- Cu(s)

Electron Loss and Gain

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Oxidation and Reduction

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Zn and Cu2+

oxidation Zn(s) Zn2+(aq) + 2e- Silvery metal

reduction Cu2+(aq) + 2e- Cu(s)

Blue orange

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Electron Transfer from Zn to Cu2+

Oxidation: electron loss

Reduction: electron gain

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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

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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

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Write the separate oxidation and reduction reactions for the following equation. 2Cs(s) + F2(g) 2CsF(s)

Each cesium atom loses an electron to form cesium ion. 2Cs(s) 2Cs+(s) + 2e− oxidation

Fluorine atoms gain electrons to form fluoride ions. F2(s) + 2e- 2F−(s) reduction

Writing Oxidation and Reduction Reactions

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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?

Learning Check

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In light-sensitive sunglasses, UV light initiates an oxidation-reduction reaction. uv light

Ag+ + Cl− Ag + Cl A. Which reactant is oxidized?

Cl − Cl− Cl + 1e− B. Which reactant is reduced?

Ag+ Ag+ + 1e− Ag

Solution

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Learning Check

Identify the substances that are oxidized and reduced in each 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 2Al 2Al3+ + 6e−

Br is reduced 2Br + 2e− 2Br−

TYPES OF CHEMICAL REACTIONS •  Chemical reactions are often classified into categories

according to characteristics of the reactions. The following is a useful classification scheme:

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Chapter 5 Chemical Reactions and Quantities 5.5

The Mole

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Collection Terms

A collection term states a specific number of items. §  1 dozen donuts = 12 donuts

§  1 ream of paper = 500 sheets

§  1 case = 24 cans

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A mole is a collection that contains §  The same number of particles as there are carbon

atoms in 12.0 g of carbon 12C. §  6.02 x 1023 atoms of an element (Avogadro’s number). 1 mole element Number of Atoms

1 mole C = 6.02 x 1023 C atoms 1 mole Na = 6.02 x 1023 Na atoms 1 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 molecules 1 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 units 1 mole K2SO4 = 6.02 x 1023 K2SO4 formula units

A Mole of a Compound

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Particle in One-Mole Samples

TABLE 5.3

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Avogadro’s number 6.02 x 1023 can be written as an equality 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

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Using Avogadro’s Number

Avogadro’s number is used to convert moles of a substance to particles. How many Cu atoms are in 0.50 mole Cu? 0.50 mole Cu x 6.02 x 1023 Cu atoms

1 mole Cu = 3.0 x 1023 Cu atoms

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Using Avogadro’s Number

Avogadro’s number is used to convert particles 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 CO2

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1. The number of atoms in 2.0 moles Al is A. 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 S is A. 1.0 mole S atoms B. 3.0 moles S atoms C. 1.1 x 1048 moles S atoms

Learning Check

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C. 1.2 x 1024 Al atoms 2.0 moles Al x 6.02 x 1023 Al atoms

1 mole Al

B. 3.0 mole S atoms 1.8 x 1024 S atoms x 1 mole S

6.02 x 1023 S atoms

Solution

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Subscripts and Moles

The subscripts in a formula give §  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

1 mole C9H8O4 = 9 moles C 8 moles H 4 moles O

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Factors from Subscripts

Subscripts used for conversion factors §  Relate moles of each element in 1 mole compound. §  For aspirin C9H8O4 can be written as:

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 O are in 0.150 mole aspirin C9H8O4? B. How many O atoms are in 0.150 mole aspirin C9H8O4?

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Solution

A. How many mole O are in 0.150 mole aspirin C9H8O4? 0.150 mole C9H8O4 x 4 moles O = 0.600 mole O 1 mole C9H8O4 subscript factor

B. How many O atoms are in 0.150 mole aspirin C9H8O4? 0.150 mole C9H8O4 x 4 moles O x 6.02 x 1023 O atoms

1 mole C9H8O4 1 mole O subscript Avogadro’s

factor Number

= 3.61 x 1023 O atoms

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Chapter 5 Chemical Reactions and Quantities

5.6 Molar Mass

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The molar mass is §  The mass of one mole of a substance. §  The atomic mass of an element expressed in grams.

Molar Mass

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Give the molar mass to the nearest 0.1 g. A. K = ________

B. Sn = ________

Learning Check

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Give the molar mass to the nearest 0.1 g. A. K = 39.1 g

B. Sn = 118.7 g

Solution

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Molar Mass of CaCl2

§  For a compound, the molar mass is the sum of the molar masses of the elements in the formula. We calculate the molar mass of CaCl2 to the nearest 0.1 g as follows.

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 K3PO4

Determine the molar mass of K3PO4 to 0.1 g.

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

K3PO4 212.3 g

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One-Mole Quantities

32.1 g 55.9 g 58.5 g 294.2 g 342.3 g

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Calculate the molar mass to the nearest 0.1g A. K2O = ______ g

B. Al(OH)3 = ______ g

Learning Check

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Calculate the molar mass to the nearest 0.1g A. K2O 2 moles K (39.1 g/mole) + 1 mole O (16.0 g/mole)

78.2 g + 16.0 g = 94.2 g B. Al(OH)3 1 mole Al (27.0 g/mole) + 3 moles O (16.0 g/mole) + 3 moles H (1.0 g/mole) 27.0 g + 48.0 g + 3.0 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) 40.0 g/mole 2) 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/mole

17C (12.0 g) + 18H (1.0 g) + 3F (19.0 g) + 1N (14.0 g) + 1 O (16.0 g) =

204 g + 18 g + 57.0 g + 14.0 + 16.0 g

Solution

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Methane CH4 known as natural gas is used in gas cook tops and gas heaters.

1 mole CH4 = 16.0 g

The molar mass of methane can be written as conversion factors. 16.0 g CH4 and 1 mole CH4

1 mole CH4 16.0 g CH4

Conversion Factors from Molar Mass

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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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Acetic acid C2H4O2 gives the sour taste to vinegar. Write two molar mass factors for acetic acid. 1 mole of acetic acid = 60.0 g acetic acid 1 mole acetic acid and 60.0 g acetic acid 60.0 g acetic acid 1 mole acetic acid

Solution

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§  Mole factors are used to convert between the grams of a substance

and the number of moles.

Calculations Using Molar Mass

Grams

Mole factor Moles

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Aluminum is often used for the structure of lightweight bicycle frames. How many grams of Al are in 3.00 moles of Al?

3.00 moles Al x 27.0 g Al = 81.0 g Al

1 mole Al mole factor for Al

Calculating Grams from Moles

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The artificial sweetener aspartame (Nutri-Sweet) C14H18N2O5 is used to sweeten diet foods, coffee and soft drinks. How many moles of aspartame are present in 225 g of aspartame?

Learning Check

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Calculate the molar mass of C14H18N2O5. (14 x 12.0) + (18 x 1.0) + (2 x 14.0) + (5 x 16.0)

= 294 g/mole Set up the calculation using a mole factor. 225 g aspartame x 1 mole aspartame

294 g aspartame mole factor(inverted) = 0.765 mole aspartame

Solution