9-3: Classifying 9-3: Classifying Chemical ReactionsChemical Reactions

9-3: Classifying 9-3: Classifying Chemical ReactionsChemical Reactions

By Ms. PachecoBy Ms. Pacheco

Direct Combination

Rxns• Two or more elements or compounds

combine to form a new compound• A + B AB• A and B can be elements or cmpds• AB is a cmpd• Ex: Na + Cl2 NaCl• Also known as “synthesis rxns”

Decomposition Reactions

• A compound breaks down into two or more elements or compounds

• AB A + B

• Ex: H2O H2 + O2

• Opposite of direct comb. rxn

• 2NaCl 2Na + Cl2

Single Replacement

Reactions•An uncombined element displaces an element that is part of a compound

•A + BX AX + B• Ex: Mg + CuSO4 Cu + MgSO4

We can predict whether or not single replacement reactions

will occur…

•Using the Activity Series of Metals (pg. 295)

•The higher up on the table the metal is, the more reactive

• Therefore, it will replace any metal underneath

For example: Will the following

reaction occur?

•Ca + MgSO4 CaSO4 + Mg

•Yes, because calcium is more active than magnesium and will replace it as the equation shows

Double Replacement

Reactions• Atoms or ions from two

different compounds replace each other

• AX + BY AY + BX• Ex: CaCO3 + HCl CaCl2 +

H2CO3

Some reactions do not fit into any of

the four main categories

• Combustion reactions:– When any thing is burned in the

presence of oxygen to produce carbon dioxide and water

– Ex: (the combustion of propane)

C3H8 + O2 CO2 + H2O