II. Five basic types of chemical reactions:

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   2PCl3

Example Zinc + Iodine zinc iodide Oxygen + Hydrogen  Water Click on pictures 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

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

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 Ammonium chloride + barium hydroxide

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

Analyzing Chemical Reactions One Reactant? no yes One Product? Decomposition no yes Next slide Synthesis

2 Ionic Compounds or Acid and Ionic Compound? yes no Double Replacement Next slide Precipitate Neutralization Gas

yes no Element and Compound? Single Replacement Hydrocarbon and O2 no Metal Halogen Metallic oxide no Combustion ????

Precipitate Gas Neutralization One Reactant? yes no One Product? Decomposition yes no Synthesis 2 Ionic Compounds or Acid and Ionic Compound? yes no Double Replacement Element and Compound? yes no Precipitate Gas Neutralization Hydrocarbon and O2? Single Replacement yes no no Combustion ????