1. “Classifying Chemical Reactions”
Notes: Ch 8-Section 3
“Classifying Chemical Reactions”

2. Classifying reactions
reasons for classification:
helps to predict what products will form
recognizing patterns can help when balancing equations
5 different types of reactions are introduced in chapter 8
additional types exist
note---some reactions can be classified as more than 1 type
note---some reactions do not “fit” any type

3. Reaction Types: Combustion Reactions
(def)- the oxidation reaction of an organic compound in which heat is released
often used to generate energy; occurs when a substance combines with oxygen releasing a large amount of energy in the form of heat and light

4. Many Combustible Compounds are Hydrocarbons
hydrocarbon (def) a compound composed of only carbon and hydrogen
the combustion of gasoline produces energy used for transportation
example: burning of propane
  C3H8 + 5O2  3CO2 + 4H2O

5. Combustion Reaction---General Pattern:
hydrocarbon + oxygen  carbon dioxide + water
Figure 9 p. 276
The complete combustion of any hydrocarbon, such as methane, yields only carbon dioxide and water

6. Combustion Reactions (cont.)
some combustible compounds are not hydrocarbons
alcohols (compounds made of carbon, hydrogen and oxygen) will also combust
example: combustion of ethanol
  CH3CH2OH + 3O2  2CO2 + 3H2O

7. Combustion Reactions (cont.)
if enough oxygen is not available, combustion reactions will be incomplete and carbon monoxide and unburned carbon (soot) will be produced along with the carbon dioxide and water

8. Reaction Types: Synthesis Reactions
(def)- a reaction in which 2 or more substances combine to form a new compound
“synthesis” (from Greek) means “to put together”
general pattern:
  A + X  AX
A, X can be elements or compounds
AX is a compound

9. Synthesis Reactions (cont.)
two elements will form a binary compound
examples:
Na + Cl  NaCl (binary ionic compound)
C + O2  CO2 (binary molecular compound)
Figure 10 p. 277
When the elements magnesium and oxygen react, they combine to form the binary compound magnesium oxide

10. Synthesis reactions (cont.)
compounds can form a ternary compound ( a compound composed of 2 or more elements)
  CaO(s) + H2O(l )  Ca(OH)2(s)
some oxides of non-metals can combine with water to produce acids
CO2(g) + H2O(l)  H2CO3(aq) (carbonic acid)

11. Reaction Types: Decomposition Reactions
(def)- a reaction in which a single compound breaks down to form two or more simpler substances
general pattern:
AX  A + X
AX is a compound
A, X can be elements or compounds
are the opposite of synthesis reactions
often need heat or electricity to proceed

12. Decomposition Reactions (cont.)
binary compounds usually decompose back into the 2 elements that compose them
example: decomposition of water  
2H2O(l) electricity 2H2(g) + O2(g)
Figure 11 p. 278
Nitrogen triiodide is a binary compound that decomposes into the elements nitrogen and iodine.

13. Decomposition Reactions (cont.)
compounds made up of 3 or more elements usually do not decompose back into those elements
example: decomposition of limestone (CaCO3)
CaCO3(s) heat CaO(s) + CO2(g)
many synthesis reactions can be reversed to become decomposition reactions

14. Reaction Types: Displacement Reactions (Single Replacement Reactions)
(def)- a reaction that occurs when 1 element replaces a similar element in a compound
general pattern:
A + BX  AX + B (or)
Y + BX  BY + X
A, B, Y and X are elements
AX, BX and BY are compounds
commonly take place in aqueous solutions
usually require a smaller amount of energy than synthesis or decomposition reactions

15. Reactivity is Ranked by Activity Series
activity series (def)- a series of elements that have similar properties and that are arranged in descending order of chemical reactivity

16. Activity Series (cont.)
elements are arranged in order, with the most active ones on top (see Table 4 p. 281 and Appendix A p. 832)
in general, any element listed can displace those below it, but not above it
allows predictions about displacement reactions to be made

17. Figure 12 page 280
Copper is the more active metal and displaces silver from the silver nitrate solution. So copper is higher on the activity series than silver is. The Cu2+ formed gives the solution a blue color

18. Reaction Types: Double-Displacement Reactions (Double Replacement Reactions)
(def)- a reaction that occurs when the ions of 2 compounds exchange places in an aqueous solution to form 2 new compounds
general pattern:
AX + BY  AY + BX
A, X, B and Y as reactants are ions
AY and BX as products are compounds

19. Double-Displacement Reactions (cont.)
takes place in aqueous solution
one of the compounds produced is usually a precipitate, an insoluble gas or a molecular compound
the other compound is often soluble and remains in solution

20. Figure 13 page 283
example: the formation of solid lead(II) iodide from an aqueous solution of potassium iodide and lead(II) nitrate
equation:
2KI(aq) + Pb(NO3)2(aq)  PbI2(s) + 2KNO3(aq)

21. Figure 13 page 283