II. Five basic types of chemical 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

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: #3: Formation of water. (If the reaction is between an acid and a base it is called a neutralization reaction.) ex. HCl  +  NaOH   NaCl  +  H2O

#2 Formation of a gas. ex. HCl + FeS - FeCl2 + H2S H2S is the only gas you need to remember.

Look for one of these three. Rewrite equation, replacing unstable compound with products. Ex. NH4Cl + Ca(OH)2  NH4OH + CaCl2 NH4Cl + Ca(OH)2  NH3  +H2O + CaCl2 Now balance the equation! Note the up arrow. You must indicate that a gas is produced!

#1 Formation of precipitate. Use Solubility Table (A solid that was not present in the reactants) Marked with (s) or  S mean soluble, or dissolved. No precipitate is formed. ALL OTHER LETTERS MEAN THAT A PRECIPITATE FORMS. Look up the formulas for your products. Whichever forms a precipitate is marked with (s) or  . Any soluble products are marked (aq). If no solid forms, write N.R. for no reaction.

Magnesium acetate + sodium carbonate  Think: It's not an acid + base. What are the products? magnesium carbonate and sodium acetate Any unstable product? Look for H2CO3, H2SO3, NH4OH Not there. Now check for a precipitate. Magnesium carbonate has a P solid forms. Finish equation with a down arrow or (s) after the magnesium carbonate.

Ammonium chloride + barium hydroxide Example Ammonium chloride + barium hydroxide

Practice Predicting Products of Ionic Reactions

Combustion of Hydrocarbons: Hydrocarbons contain hydrogen and carbon. Some also have oxygen. When a hydrocarbon is burned with sufficient oxygen supply, the products are always carbon dioxide and water vapor. 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

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: ex. Fe  +  CuSO4   FeSO4  +  Cu

2. Replacement of hydrogen in water by an active metal. ex. 2Na  +  2H2O   2NaOH  +  H2 Only one hydrogen is replaced, leaving an hydroxide ion.

Only these metals will react with water, producing hydrogen gas and metallic hydroxide.

3. Replacement of hydrogen in acids by active metals. ex. Zn  +  2HCl   ZnCl2  +  H2

Only these metals will react with acids, producing hydrogen gas and metallic hydroxide.

ex. Cl2  +  2NaBr   2NaCl  +  Br2 The halogen is replaced, NOT the metal! The halogen activity series is Group 17 on the Periodic Table.

Examples

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

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 ????