1. Classification of Chemical Reactions
Notes

2. Composition (also called combination or synthesis)
Two reactants combine to form one product
A + B  AB
Example: 3Na + P  Na3P
Helpful hints
An element plus another element will always be composition; if there is only one product, it has to be composition
Note that composition reactions are redox reactions

3. Decomposition
One reactant breaks down (decomposes) into two (or more) products
AB  A + B
Example: 2HgO  2Hg + O2
Helpful hints
If there is only one reactant, it has to be decomposition
Note that decomposition reactions are redox

4. Single Replacement (Redox)
An element takes the place of a similar element (in terms of charge) in a compound
A + BC  AC + B or
D + BC  BD + C
Examples: 3Na + AlCl3  3NaCl + Al
F2 + 2NaCl  2NaF + Cl2
Helpful hints
An element plus an ionic compound will usually be single replacement; there are always 2 reactants and 2 products

5. Single Replacement continued
Hydrogen is often a participant in redox single replacement reactions
The activity series or a table of standard reduction potentials must be used to determine if a s.r. redox reaction will occur

6. Double Replacement (Ionic)
The + and – ions in two ionic compounds switch partners
AB + CD  AD + CB
Example:
2Na3PO4 + 3CaCl2  Ca3(PO4)2 + 6NaCl
Helpful hints
Two ionic compounds yield two ionic compounds; remember a + ion always goes with a – ion and the + is written first in the formulas

7. Combustion
A hydrocarbon (a compound made up of carbon, hydrogen, and sometimes oxygen) reacts with oxygen, or burns, to give carbon dioxide plus water
CxHy + O2  CO2 + H2O or
CxHyOz + O2  CO2 + H2O
Example: CH4 + 2O2  CO2 + 2H2O
Helpful hints
Oxygen is always a reactant and the products are always carbon dioxide and water!
These are also redox reactions