1. Classification of Chemical Reactions

2. Types of Chemical Reactions
Synthesis
Decomposition
Single Replacement
Double Replacement
Combustion

3. Synthesis Reactions
A reaction in which two or more simple substances (elements or compounds) react to form one new substance.
A + B  AB
Example: 2H2 + O2  2H2O
CaO + CO2  CaCO3

4. Decomposition Reactions
A reaction in which one substance breaks down into two or more simple substances
AB  A + B
Example: 2H2O2  2H2O + O2
2KClO3  2KCl + 3O2

5. Single Replacement Reactions
A reaction in which an uncombined element replaces another element in a compound
A + BC  AC + B
“Like replaces like” – metals replace metals and nonmetals replace nonmetals

6. Single Replacement Reactions (continued)
Examples:
Mg + CuSO4  MgSO4 + Cu
(Mg and Cu are both metals)
Cl2 + NaBr  NaCl + Br2
(Cl and Br are both nonmetals)
In order for the reaction to take place, the uncombined element must be more reactive than the ion it is replacing.

7. Reactivity Table
Most Active Metals Li Rb K Ca Na Mg Al Mn Zn Fe Ni Sn Pb Cu Ag
Least Active Metals Pt Au
Most Active Nonmetals F Cl Br I
Least Active Nonmetals

8. Which of the following reactions can take place?
I2 + NaF  F2 + NaI
Mg + HCl  MgCl2 + H2
Cu + MgSO4  CuSO4 + Mg
K + NaOH  KOH + Na

9. Double Replacement Reactions
A reaction in which two positive ions replace each other in compounds
AB + CD  AD + CB
In order for this type of reaction to occur, one of the following must happen: a precipitate is formed, a gas is formed, or one of the products must be covalent.

10. Double Replacement Reactions (continued)
Examples:
Na2S + Cu(NO3)2 CuS+ 2NaNO3
(a precipitate is formed)
2NaCN + H2SO4 2HCN + Na2SO4
(a gas is formed)
NaOH + HCl  NaCl + H2O
(a covalent compound is formed)

11. Combustion Reaction
A reaction in which a hydrocarbon reacts with oxygen to produce carbon dioxide and water
CxHy + O2  CO2 + H2O
Example: CH4+ 2O2 CO2 + 2H2O
C6H12O6 + 6O2  6CO2 + 6H2O

12. Review
Classify each of the following reactions by type and then balance the equation:
Pb(NO3)2 + K2CrO4PbCrO4+ KNO3
Cl2 + KI  KCl + I2
C3H6 + O2  CO2 + H2O
Al(OH)3  Al2O3 + H2O
Li + O2  Li2O
HCl + Fe2O3  FeCl3 + H2O
MgCO3  MgO + CO2
Ba(CN)2 + H2SO4  HCN + BaSO4

13. Classifying Reactions Based on Energy Changes
Exothermic reactions are reactions in which heat/energy is released
Example:
2C4H O2  8CO2 + 10H2O
The container often feels warm during exothermic reactions
reactions involving explosions and burning are examples

14. Classifying Reactions Based on Energy Changes (continued)
Endothermic reactions are reactions in which heat/energy is absorbed
Example:
6CO2 + 6H2O C6H12O6 + 6CO2
(photosynthesis)
NaHCO3 + HCl  NaCl + H2O + CO2
The container often feels cold during endothermic reactions
Reactions involving cooking or heating are often examples

15. Review Baking a cake Exploding dynamite Burning a piece of paper
Identify each of the following as either exothermic or endothermic:
Baking a cake
Exploding dynamite
Burning a piece of paper
A chemical ice pack
Hand warmers