Main types of Chemical Reactions
A. Composition or Synthesis Reaction-
Element or compounds react to form JUST ONE PRODUCT.
4 Al + 3O
2

2Al
2
O
3
N
2
O
5
+ H
2
O

2HNO
3
1. A Group IA or IIA metal may combine with a nonmetal to make a salt .
Ex. A piece of lithium metal is dropped into a container of nitrogen gas.
Li + N
2

Li
3
N
2. Two nonmetals may combine to form a molecular compound .
Ex. P
4
+ 6Cl
2

4PCl
3
limited Cl
P
4
+ 10Cl
2
 4PCl
5
excess Cl
3. When an element combines with a compound, you can usually sum up all of the elements on the product side.
Ex. PCl
3
+ Cl
2

PCl
5
4. Two compounds combine to form a single product .
Ex. Sulfur dioxide gas is passed over solid calcium oxide.
SO
2
+ CaO  CaSO
3
5. A metallic oxide plus carbon dioxide yields a metallic carbonate . (Carbon keeps the same oxidation state)
Na
2
O+ CO
2

Na
2
CO
3
6. A metallic oxide plus sulfur dioxide yields a metallic sulfite . (Sulfur keeps the same oxidation state)
Na
2
O + SO
3

Na
2
SO
3
7. A metallic oxide plus water yields a metallic hydroxide .
Na
2
O + H
2
O

NaOH
8. A nonmetallic oxide plus water yields an acid .
NO
2
+ H
2
O

HNO
3
B. Decomposition Reaction-
Start off with JUST ONE REACTANT. It breaks down. Heat, electrolysis, or a catalyst is usually necessary.
2K(ClO
Ca(CO
3
)
3
)


2KCl + 3O
CaO + CO
2
2

1. A compound may break down to produce two elements .
Ex. Molten sodium chloride is electrolyzed.
2NaCl (l)

2Na + Cl
2
2. A compound may break down to produce an element and a compound .
Ex. A solution of hydrogen peroxide is decomposed catalytically.
H
2
O
2

H
2
O + O
2
3. A compound may break down to produce two compounds .
Ex. Solid magnesium carbonate is heated.
MgCO
3

MgO + CO
2
4. Metallic carbonates break down to yield metallic oxides and carbon dioxide .
Na
2
CO
3

NaO + CO
2
5. Metallic chlorates break down to yield metallic chlorides and oxygen .
NaClO
3

NaCl + O
2
6. Sulfurous acid decomposes into water and sulfur dioxide .
H
2
SO
3

H
2
O + SO
2
7. Carbonic acid decomposes into water and carbon dioxide .
H
2
CO
3

H
2
O + CO
2
C. Single Replacement Reaction –
1. A metal bumps a less active metal out of a compound .
Ca + 2Ag(NO
3
)(aq)

2Ag + Ca(NO
3
)
2
(aq)
2. A nonmetal bumps a less active nonmetal out of a compound .
Cl
2
+ 2KI (aq)

I
2
+ 2KCl(aq)
3. Active metals replace less active metals or hydrogen from their compounds in aqueous solution. Use an activity series or a reduction potential table to determine activity. The more easily oxidized metal replaces the less easily oxidized metal. The metal with the most negative reduction potential will be the most active.
Ex. Magnesium turnings are added to a solution of iron(III) chloride.
Mg + Fe
3+ 
Fe + Mg
2+
Ex. Sodium is added to water.
Na + H
2
O

Na
+
+ OH
-
+ H
2
4. Active nonmetals replace less active nonmetals from their compounds in aqueous solution. Each halogen will displace less electronegative (heavier) halogens from their binary salts.
Ex. Chlorine gas is bubbled into a solution of potassium iodide.
Cl
2
+ I

I
2
+ Cl
-

D. Double Replacement-
The metals in 2 ionic substances trade places.
Pb(NO
3
)
2
(aq) + 2KI(aq
)

PbI
2
(s) + 2K(NO
3
)(aq)
1. Two compounds react to form two new compounds. No changes in oxidation numbers occur. All double replacement reactions must have a "driving force" that removes a pair of ions from solution.
A. Formation of a precipitate : A precipitate is an insoluble substance formed by the reaction of two aqueous substances. Two ions bond together so strongly that water can not pull them apart. You must know your solubility rules to write these net ionic equations!
Ex. Solutions of silver nitrate and lithium bromide are mixed.
Ag + + Br 
AgBr(s)
B. Formation of a gas: Gases may form directly in a double replacement reaction or can form from the decomposition of a product such as H
2
CO
3
or H
2
SO
3
.
Ex. Excess hydrochloric acid solution is added to a solution of potassium sulfite.
H
+
+ SO
3
2- 
H
2
O + SO
2
(g)
Ex. A solution of sodium hydroxide is added to a solution of ammonium chloride.
OH
-
+ NH
4
+ 
NH
3
+ H
2
O
C. Formation of a molecular substance : When a molecular substance such as water or acetic acid is formed, ions are removed from solution and the reaction "works".
Ex. Dilute solutions of lithium hydroxide and hydrobromic acid are mixed.
OH
-
+ H
+ 
H
2
O (HBr, HCl, and HI are strong acids)
E. Combustion Reaction-
2C
2
H
6
+ 7O
2

4CO
2
+ 6H
2
O
1. Elements or compounds combine with oxygen. Nonmetallic hydrides combine with oxygen to form oxides and water.
Ex. Carbon disulfide vapor is burned in excess oxygen.
CS
2
+ O
2

CO
2
+ SO
2
2. Hydrocarbons or alcohols combine with oxygen to form carbon dioxide and water .
Ex. Ethanol is burned completely in air.
C
2
H
5
OH + O
2

CO
2
+ H
2
O
3. Nonmetallic sulfides combine with oxygen to form oxides and sulfur dioxide .
Ex. Carbon disulfide vapor is burned in excess oxygen.
CS
2
+ O
2

CO
2
+ SO
2