Chapter 8

Types of Reactions

I. Introduction

A. There are 5 basic reaction types:

1) Combination

2) Decomposition

3) Single Replacement

4) Double Replacement

5) Combustion

B. Three different presentations of equations

are possible:

1) Molecular equation

2) ionic equation

3) net ionic equation*

* Net ionic equations are only relevant for

single and double replacements

C. A “net ionic equation” eliminates those

equation members who are identical on the

reactant side and product side

1) these are called “spectator ions”

2) If no ions are present, then all members

are kept in the final equation

Ex: 2 KClO3 ---> 2 KCl + 3 O2

(all members are kept in final equation)

[Only molecular equation is written]

Ex: Zn + 2 HCl(aq) --> ZnCl2(aq) + H2

Zn + 2 H+ + 2 Cl- --> Zn+2 + 2 Cl- + H2

Zn + 2 H+ --> Zn+2 + H2

[ the “2 Cl-” were eliminated because they did not change from reactants to products]

Ex:

HCl(aq) + NaOH (aq) --> NaCl (aq) + H2O (aq)

H+ + Cl- + Na+ + OH- --> Na+ + Cl- + H2O

H+ + OH- --> H2O

[ the Cl- and Na+ were eliminated as they did not change ]

II. Combination Reactions

A. ONLY ONE PRODUCT is formedB. Possible reactants can be:

1) element + element

ex: 2 H2 + O2 --> H2O

ex: 2 Na + Cl2 --> 2 NaCl

2) nonmetal oxides + water --> acids

ex: SO3 + H2O --> H2SO4

3) metal oxides + water --> bases

ex: MgO + H2O --> Mg(OH)2

A. ONLY ONE REACTANT

B. Types of reactants include:

1) chlorates --> oxygen + metal chloride

ex: 2 KClO3 --> 3 O2 + 2 KCl

2) carbonate --> carbon dioxide + metal oxide

ex: CaCO3 --> CO2 + CaO

ex: 2 NaHCO3 --> CO2 + Na2CO3 + H2O

III. Decomposition Reactions

3) hydroxides --> water + metal oxide

ex: Mg(OH)2 --> H2O + MgO

4) Hydrogen peroxide --> oxygen + water

ex: 2 H2O2 --> O2 + 2 H2O

5) Binary metal oxides --> oxygen + metal

ex: 2 HgO --> O2 + 2 Hg

A. Element + compound --> element + compound

B. Types of single replacement:

1) metal + acid --> hydrogen + salt

ex: Zn + HCl(aq) --> H2 + ZnCl2 (aq)

Note: these metals do not produce H2:

Cu Ag Hg Pt Au

IV. Single Replacement Reactions

2) Metal + salt --> metal + salt

ex: Cu + 2 AgNO3 (aq) --> 2 Ag + Cu(NO3)2 (aq)

3) Metal + water --> hydrogen + base

ex: 2 Na + 2 H2O --> H2 + 2 NaOH(aq)

Note: DO NOT produce H2 + Na2O; Think of it as:

ex: 2 Na + 2 HOH --> H2 + 2 NaOH(aq)

4) Non metal + salt --> non metal + salt

F2 + 2 NaCl --> Cl2 + 2 NaF

A. Involves 2 compounds reacting --> 2 new

compounds formed

B. Subscripts depend on partner ions

C. Solubility rules MUST be used to predict

precipitated products

D. Products include precipitates, water, or

gases

IV. Double Replacement Reactions

E. Examples with various products: 1) precipitated products (using solubility rules)

ex: 2 NaI + Pb(NO3)2 --> 2 NaNO3 + PbI2

AgNO3 + NaCl --> NaNO3 + AgCl

2) water is formed (neutralization reactions)

ex: HCl + NaOH --> NaCl + H2O

acid + base --> salt + water

3) Gases are formed… these products break down into these gases:

a) NH4OH --> NH3 + H2O

b) H2CO3 --> CO2 + H2O

c) H2SO3 --> SO2 + H2O

Ex: NH4Cl + NaOH --> NaCl + NH3 + H2O

Na2CO3 + 2 HCl --> 2 NaCl + CO2 + H2O

Na2SO3 + HCl --> NaCl + SO2 + H2O

A. Use oxygen as a reactant

B. Every element bonds with an oxygen

Ex: CH4 + 2 O2 --> CO2 + 2 H2O

[All “CxHy” compounds produce CO2 + H2O]

Ex: CS2 + 2 O2 --> CO2 + 2 SO2

V. Combustion Reactions

VI. Advanced Equation Writing

A. All equations will be given in a sentence without any chemical symbols

ex: Magnesium ribbon is burned in air

you write: Mg + O2 -->

B. Solids are NEVER written as ions

ex: “Solid sodium carbonate is added to…”

Na2CO3 + ….

The 7 Strong acids:

HCl

HBr

HI

HNO3

HClO3

HClO4

H2SO4

C. Strong acids ALWAYS ionize

Weak acids NEVER ionize

D. Solutions always ionize…(but not weak acids)

F. Phases are not required (ex: aq, s, l, g)

E. Soluble products always ionize

Examples:

1) Aluminum metal is added to a solution of hydrochloric acid

Procedure:

2 Al + 6 HCl --> 2 AlCl3 + 3 H2

2 Al + 6 H+ + 6 Cl- --> 2 Al+3 + 6 Cl- + 3 H2

FINAL ANS:

2 Al + 6 H+ --> 2 Al+3 + 3 H2

Examples:

2) Sodium oxide powder is added to water

Procedure:

Na2O + H2O --> 2 NaOH

Na2O + H2O --> 2 Na+ + 2 OH-

FINAL ANS:

Na2O + H2O --> 2 Na+ + 2 OH-

Examples:

3) Solutions of barium acetate and sodium sulfate are mixed

Procedure:

Ba(C2H3O2)2 + Na2SO4 --> BaSO4 + 2 NaC2H3O2

Ba+2 + 2 C2H3O2- + 2 Na+ + SO4

-2 --> BaSO4 + 2 Na+ + 2 C2H3O2-

FINAL ANS:

Ba+2 + SO4-2 --> BaSO4

Examples:

3) Solid sodium hydroxide is added to a solution of acetic acid

Procedure:

NaOH + HC2H3O2 --> NaC2H3O2 + H2O

NaOH + HC2H3O2 --> Na+ + C2H3O2- + H2O

FINAL ANS:

NaOH + HC2H3O2 --> Na+ + C2H3O2- + H2O