Type of Reactions Chemical reactions are classified into several general types Combination...

Type of Reactions

Chemical reactions are classified into several general types

Combination (Synthesis)

Decomposition

Single Replacement

Double Replacement (Metathesis)

1

Combination (Synthesis)

Two or more elements or simple compounds combine to form (synthesize) one product

A + B AB

2Mg + O2 2MgO

2Na + Cl2 2NaCl

SO3 + H2O H2SO4

2

Decomposition

One substance is broken down (split) into two or more simpler substances.

AB A + B

2HgO 2Hg + O2

2KClO3 2KCl + 3 O2

3

Learning Check R1

Classify the following reactions as

1) combination or 2) decomposition:

___A. H2 + Br2 2HBr

___B. Al2(CO3)3 Al2O3 + 3CO2

___C. 4 Al + 3C Al4C3

4

Solution R1

Classify the following reactions as

1) combination or 2) decomposition:

_1_A. H2 + Br2 2HBr

_2_B. Al2(CO3)3 Al2O3 + 3CO2

_1_C. 4 Al + 3C Al4C3

5

Single Replacement

One element takes the place of an element in a reacting compound.

A + BC AB + C

Zn + 2HCl ZnCl2 + H2

Fe + CuSO4 FeSO4 + Cu

6

Double Replacement

Two elements in reactants take the place of each other

AB + CD AD + CB

AgNO3 + NaCl AgCl + NaNO3

ZnS + 2HCl ZnCl2 + H2S

7

Learning Check R2

Classify the following reactions as

1) single replacement

2) double replacement

__A. 2Al + 3H2SO4 Al2(SO4)3 + 3H2

__B. Na2SO4 + 2AgNO3 Ag2SO4 + 2NaNO3

__C. 3C + Fe2O3 2Fe + 3CO8

Solution R2

Classify the following reactions as

1) single replacement

2) double replacement

1_A. 2Al + 3H2SO4 Al2(SO4)3 + 3H2

2_B. Na2SO4 + 2AgNO3 Ag2SO4 + 2NaNO3

1_C. 3C + Fe2O3 2Fe + 3CO9

Combustion

A reaction in which a compound (often

carbon) reacts with oxygen

C + O2 CO2

CH4 + 2O2 CO2 + 2H2O

C3H8 + 5O2 3CO2 + 4H2O

C6H12O6 + 6O2 6CO2 + 6H2O

10

Learning Check R3

Balance the combustion equation

___C5H12 + ___O2 ___CO2 + ___H2O

11

Solution R3

Balance the combustion equation

1 C5H12 + 8 O2 5 CO2 + 6 H2O

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Oxidation and Reduction

Reactions that involve a loss or gain of electrons

Occurs in many of the types of reactions and combustion

Important in food metabolism, batteries, rusting of metals

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Requirements for Oxidization-Reduction

Electrons are transferred

Two processes occur

Oxidation = Loss of electrons (LEO)

Zn Zn2+ + 2e-

Reduction = Gain of electrons (GER)

Cu2+ + 2e- Cu

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Balanced Red-Ox Equations

Combine the oxidation and reduction reactions to make

Loss of electrons = Gain of electrons

Zn + Cu2+ + 2e- Zn2+ + 2e- + Cu

Zn + Cu2+ Zn2+ + Cu

15

Learning Check R3

Identify the following as an 1) oxidation or a reduction process:

__A. Sn Sn4+ + 4e-

__B. Fe3+ + 1e- Fe2+

__C. Cl2 + 2e- 2Cl-

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Solution R3

Identify the following as an 1) oxidation or a reduction process:

1_ A. Sn Sn4+ + 4e-

2_ B. Fe3+ + 1e- Fe2+

2_ C. Cl2 + 2e- 2Cl-

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RedoxRedox• REDOX stands for REDuction/OXidation• Oxidation refers to a loss of electrons• Reduction refers to a gain of electrons

• LEO –GER• Loss Electrons = Oxidation• Gain Electrons = Reduction• OIL-RIG • Oxidation Is Loss • Reduction Is Gain

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oxidation = loss of e–

X X+ + e–

reduction = gain of e–

X + e– X–

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Oxidation numbersOxidation numbers• We will see that there is a simple way to keep

track of oxidation and reduction• This is done via “oxidation numbers”• An oxidation number is the charge an atom

would have if electrons in its bonds belonged completely to the more electronegative atom

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RulesRules 1.Any element, when not combined with atoms

of a different element, has an oxidation # of zero. (O in O2 is zero)

2.Any simple monatomic ion (one-atom ion) has an oxidation number equal to its charge (Na+ is +1, O2– is –2)

3.The sum of the oxidation numbers of all of the atoms in a formula must equal the charge written for the formula. (if the oxidation number of O is –2, then in CO3

2– the oxidation number of C is +4)

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4. In compounds, the oxidation # of IA metals is +1, IIA is +2, and aluminum (in IIIA) is +3

5. In ionic compounds, the oxidation # of a nonmetal or polyatomic ion is equal to the charge of its associated ion. (CuCl2, Cl is –1)

6.F is always –1, O is always –2 (unless combined with F), H is usually +1

totalOx.#

Rules Rules

+1+1

-2-6+5

+5 +1+2

-2-14+12

+6 +1+6

-2-2-4

-2 -1-1+1

+1H N O 3 C2H6OK2Cr2O7 AgI

+1+2

-2-8+5

+5H2PO4

–

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Writing Chemical Equations

11.1

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Classifying Reactions

– Combination Reactions• A combination reaction is a chemical change in

which two or more substances react to form a single new substance.

11.2

24

Classifying Reactions

– Decomposition Reactions• A decomposition reaction is a chemical change

in which a single compound breaks down into two or more simpler products.

11.2

25

Classifying Reactions

– Single-Replacement Reactions• A single-replacement reaction is a chemical

change in which one element replaces a second element in a compound.

11.2

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Classifying Reactions• The activity series of

metals lists metals in order of decreasing reactivity.

• Generally, the higher in the periodic table, the more reactive.

11.2

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28

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Classifying Reactions

– Double-Replacement Reactions• A double-replacement reaction is a chemical

change involving an exchange of positive ions between two compounds.

11.2

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31

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Predicting the Formation of a Precipitate

11.3

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Classifying Reactions

– Combustion Reactions• A combustion reaction is a chemical change in

which an element or a compound reacts with oxygen, often producing energy in the form of heat and light.

11.2

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Net Ionic Equations

• A complete ionic equation is an equation that shows dissolved ionic compounds as dissociated free ions.

11.3

35

Net Ionic Equations

• An ion that appears on both sides of an equation and is not directly involved in the reaction is called a spectator ion.

• The net ionic equation is an equation for a reaction in solution that shows only those particles that are directly involved in the chemical change.

11.3

36

Net Ionic Equations

– A net ionic equation shows only those particles involved in the reaction and is balanced with respect to both mass and charge.

11.3

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Net Ionic Equations

• Sodium ions and nitrate ions are not changed during the chemical reaction of silver nitrate and sodium chloride so the net ionic equation is

11.3

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39

40

41

42

• Will a precipitate form when a sodium carbonate solution is mixed with a barium nitrate solution?

11.3

43

Predicting the Formation of a Precipitate

• Sodium nitrate is soluble but barium carbonate is insoluble. The net ionic equation is

11.3

44