II. Five basic types of chemical reactions:

A. Synthesis (composition)

B. Decomposition

C. Single Replacement

D. Ionic or Double Replacement

E. Combustion

A. Synthesis (composition):

two or more elements or compounds may combine to form a more complex compound.

Basic form: A  +  X  AX

Examples of synthesis reactions

Metal  +  oxygen metal oxide

ex. 2Mg  +  O2  2MgO

Nonmetal  +  oxygen  nonmetallic oxide

ex. C  +   O2  CO2

Metal oxide  +  water  metallic hydroxide

ex. MgO  +   H2O  Mg(OH)2

Nonmetallic oxide  +  water  acid

ex. CO2  +  H2O   H2CO3

Metal + nonmetal  salt

ex. 2 Na  +  Cl2  2NaCl

A few nonmetals combine with each other. ex. 2P  +  3Cl2  2PCl3

What do all of these have in common?

2Mg  +  O2  2MgO

C  +   O2  CO2

CO2  +  H2O   H2CO3

MgO  +   H2O  Mg(OH)2

2 Na  +  Cl2  2NaCl

2P  +  3Cl2  2PCl3Only one product is formed.

Example(from Chemistry Interactive 2.0 CD, disk 1)

Zinc + Iodine zinc iodide

Oxygen + Hydrogen Water

Practice Predicting Products of Synthesis Reactions

B. Decomposition:

A single compound breaks down into its component parts or simpler compounds.

Basic form: AX A  +  X

Examples of decomposition reactions:

Metallic carbonates, when heated, form metallic oxides and CO2 .

ex. CaCO3  CaO  +  CO2

Most metallic hydroxides, when heated, decompose into metallic oxides and water.

ex. Ca(OH)2  CaO  +  H2O

Metallic chlorates, when heated, decompose into metallic chlorides and oxygen.

ex. 2KClO3  2KCl  +  3O2

Some acids, when heated, decompose into nonmetallic oxides and water.

ex. H2SO4  H2O  +  SO3

Some oxides, when heated, decompose.

ex. 2HgO  2Hg  +  O2

Some decomposition reactions are produced by electricity.

ex. 2H2O   2H2  +  O2

ex. 2NaCl   2Na  +  Cl2

What do all of these have in common?

CaCO3  CaO  +  CO2

Ca(OH)2  CaO  +  H2O

2KClO3  2KCl  +  3O2

H2SO4  H2O  +  SO3

2HgO  2Hg  +  O2

2H2O   2H2  +  O2

They have only one reactant.

Example

Decomposition of ammonium dichromate

Practice Predicting Products of Decomposition Reactions

C. Single Replacement:

a more active element takes the place of another element in a compound and sets the less active one free.

Basic form: A  +  BX  AX  +  B

 or

AX  +  Y  AY + X

Examples of replacement reactions:

Replacement of a metal in a compound by a more active metal.

ex. Fe  +  CuSO4  FeSO4  +  Cu

Replacement of hydrogen in water by an active metal.

ex. 2Na  +  2H2O  2NaOH  +  H2

ex. Mg  +  H2O  MgO  +  H2

Replacement of hydrogen in acids by active metals.

ex. Zn  +  2HCl  ZnCl2  +  H2

Replacement of nonmetals by more active nonmetals.

ex. Cl2  +  2NaBr  2NaCl  +  Br2

Examples(use Disk 2)

Practice Predicting Products of Replacement Reactions

D. Ionic or Double Replacement:

occurs between ions in aqueous solution.

A reaction will occur when a pair of ions come together to produce at least one of the following:

a precipitate a gas water or some other non-ionized substance.

Basic form: AX  + BY    AY  +  BX

Examples of ionic reactions:

Formation of precipitate.

ex. NaCl  +  AgNO3  NaNO3  +  AgCl

ex. BaCl2  +  Na2 SO4  2NaCl  +  BaSO4

Formation of a gas.

ex. HCl  +  FeS -  FeCl2  +  H2S

Formation of water. (If the reaction is between an acid and a base it is called a neutralization reaction.)

ex. HCl  +  NaOH  NaCl  +  H2O

Formation of a product which decomposes.

ex. CaCO3  +  HCl

 CaCl2  +  CO2  +  H2O

Ammonium chloride + barium hydroxide

Example

Practice Predicting Products of Ionic Reactions

Combustion of Hydrocarbons:

When a hydrocarbon is burned with sufficient oxygen supply, the products are always carbon dioxide and water vapor.

If the hydrocarbon has an even number of carbons, start with a coefficient of 2 CxHy

Balance in this order: C, H, O

If the supply of oxygen is low or restricted, then carbon monoxide will be produced.

This is why it is so dangerous to have an automobile engine running inside a closed garage or to use a charcoal grill indoors.

NOTE:

The phrase "To burn" means to add oxygen unless told otherwise.

(CxHy)  +  O2  CO2  +  H2O

ex. CH4  +  2O2  CO2  +  2H2O

ex. 2C4H10   13O2  8CO2  + 10H2O

Analyzing Chemical ReactionsOne Reactant?

yes

DecompositionNext slide

no

2 Ionic Compounds or Acid and Ionic Compound?

yes no

Double Replacement

Precipitate

Next slide

Neutralization Gas

Element and Compound?

yes no

Single Replacement

Metal

Hydrocarbon and O2

yesno

Combustion

Synthesis

no

Halogen Metallic oxide

One Reactant?yes

Decomposition

2 Ionic Compounds or Acid and Ionic Compound?yes

Double Replacement

Precipitate Gas Neutralization

no

Element and Compound?

yes no

Single Replacement

Hydrocarbon and O2?

Combustion

yesnono

Synthesis

no

Metal Halogen Metallic oxide

yes