1. Classifying Chemical Reactions
Chapter 8

2. Types of Chemical Rxns Classifying reactions
There are 5 general types of reactions
Combination (aka synthesis or composition)
Decomposition
Single-replacement
Double-replacement (acid-base & precipitation)
Combustion
Not all chemical reactions fit neatly into only one of these classes - sometimes, one reaction may fit 2 or 3 different types (or none of the types)

3. Combination reactions (synthesis)
Two or more substances combine to form ONE product. The product will always be a compound
Metal + nonmetal  ionic compound
EX: 2Na + Cl2  2NaCl
Nonmetal + nonmetal  molecular compound
Sometimes, 2 nonmetals may produce more than one product
S + O2  SO2
2S + 3O2  2 SO3

4. Decomposition reactions
ONE single compound is broken down into two or more products
The products can be any combination of elements or compounds
It is usually very difficult to predict the products of decomposition reactions
Most decomposition reactions usually require energy in the form of heat, light, or electricity
EX: 2KClO3 + heat  2KCl + 3O2
CaCO3 + heat  CaO + CO2

5. Single-replacement reactions
A free element replaces an element within an ionic compound (or an acid)
Also known as single-displacement reactions
Whether one metal will replace another can be determined by the chemical reactivities of the two metals
The activity series lists metals in order of decreasing reactivity
A metal can replace any metal listed below it on the series
EX: Zn + CuSO4  Cu + ZnSO4
Zn + Na2SO4  No reaction

6. Single-replacement reactions (cont.)
A halogen can also replace another halogen in a compound
This replacement is usually limited to halogens
The activity of halogens decreases as you move down the group
Fluorine can replace any of the halogens, chlorine can replace any halogen beneath it, etc.
EX: 2NaBr + Cl2  2NaCl + Br2
NaBr + I2  No reaction

7. Double-replacement reactions
Precipitation reactions involve an exchange of positive ions between two ionic compounds (or an ionic compound and an acid)
Generally take in aqueous solution
Characterized by the formation of a precipitate (a solid formed from mixing two aqueous compounds)
EX: BaCl2(aq) + Na2SO4(aq)  BaSO4(s) + NaCl(aq)

8. Double-replacement reactions
Acid-Base reactions involve an exchange of positive ions between an acid and a metal hydroxide
Generally take in aqueous solution
Characterized by the formation of water and a salt (an ionic compound that is not an oxide or hydroxide)
EX: Ba(OH)2(aq) + H2SO4(aq)  BaSO4(s) + H2O(l)

9. Combustion reactions
An element or compound reacts with oxygen, often producing energy in form of heat and light
These reactions commonly involve hydrocarbons, compounds of H and C
The complete combustion of a hydrocarbon produces CO2 and H2O
If the supply of O2 is insufficient during the reaction, combustion will be incomplete
A large amount of heat is usually released
EX: C3H8 + 5O2  3CO2 + 4H2O + heat