Reaction Type
Notes
Reaction Type Notes
 Most chemical reactions can
be categorized into one of five
types.
 You can usually identify the
reaction type by looking at the
reactants. Once the type of
reaction is identified, we can
predict the products.
Reaction Type Notes
Chemists classify reactions in order
to organize the many types:
• A synthesis reaction is a reaction
in which two or more substances
react to produce a single product.
• General form:
A + B  AB or A + BC  ABC or
AB + CD  ABCD
Types of Chemical Reactions
• When two elements react, the
reaction is always a synthesis
reaction.
Reaction Type Notes
Example: 2 H2 + O2  2
H2O
Reaction Type Notes
Synthesis:
 To predict the products: for binary
compounds, put elements together
and balance the total charges.
Otherwise, just combine.
 These reactions generally happen
spontaneously, and are generally
exothermic (release energy).
Types of Chemical Reactions
• In a combustion reaction, oxygen
combines with another substance
and releases energy in the form of
heat and light.
• Heated hydrogen reacts with oxygen
to produce heat and water in a
combustion reaction. This is also a
synthesis reaction.
Reaction Type Notes
 Hydrocarbon combustion—a
specific case of combustion in
which a hydrocarbon (a substance
only containing carbon and
hydrogen) reacts with oxygen to
form carbon dioxide and water
 General form: CxHy + O2  CO2 +
H2O
Reaction Type Notes
Example:
2C2H6 + 7O2  4CO2 + 6H2O
Reaction Type Notes
Hydrocarbon Combustion:
 To predict products:
 At least carbon dioxide and
water. Always exothermic, but
often requires a large activation
energy, keeping it from
happening spontaneously.
Decomposition Reactions
• A decomposition reaction is
one in w
hich a single
compound breaks down into
two or more elements or new
compounds.
• Decomposition reactions often
require an energy source, such
as heat, light, or electricity, to
occur and be maintained.
• General form: AB  A + B
Reaction Type Notes
Example: 2H2O2  2 H2O + O2
(Needs a catalyst—Potassium Iodide)
Reaction Type Notes
Decomposition:
To predict the products:
 Binary compounds separate into
their two elements.
 You will be given a handout to
predict others.
 Generally not spontaneous, and
generally endothermic.
Replacement Reactions
• A reaction in which the
atoms of one element
replace the atoms of another
element in a compound is
called a single replacement
reaction.
• General form: A + BX → AX +
B
Replacement Reactions (cont.)
• A metal will not
always replace a
metal in a compound
dissolved in water
because of differing
reactivities.
• An activity series
can be used to
predict if reactions
will occur.
Replacement Reactions (cont.)
• Anions can replace anions in
compounds. Halogens
frequently replace other
halogens in replacement
reactions.
• Halogens also have different
reactivities, like metallic
elements. There is a separate
activity series for anions.
Reaction Type Notes
Example: 2 Na + 2 H(OH) 
2 Na(OH)+ H2
Reaction Type Notes
Single displacement:
 To predict the products: The element
switches places with the element of
similar charge within the compound.
 If the element is more reactive, then the
one it attempts to replace, then the
reaction will be spontaneous and
exothermic. Otherwise, it will not be
spontaneous and will be endothermic
(require the input of energy).
Reaction Type Notes
Activity Series:
Most Active Cations 
Least Active
 Lithium
 Rubidium
 Potassium
 Barium
 Calcium
 Sodium
 Magnesium
 Aluminum
 Manganese












Zinc
Chromium
Iron
Nickel
Tin
Lead
Hydrogen
Copper
Mercury
Silver
Platinum
Gold
*Red not included in book values
Reaction Type Notes
Activity Series:
Most Active Anions 
Least Active
 Fluorine
 Oxygen
 Chlorine
 Nitrogen
 Bromine
 Iodine







Sulfur
Selenium
Astatine
Phosphorus
Tellurium
Arsenic
Polonium
*Red not included in book
values
Reaction Type Notes
• Double replacement reactions
occur when ions are exchanged
between two compounds.
• This figure shows the form of a
double replacement equation.
Reaction Type Notes
Double displacement:
To predict the products:
 Like charged particles switch places
 Both compounds are initially stable and
so reactions will usually not be
spontaneous as solids. If compounds
can be dissolved and dissociated
(broken apart) then the reaction will
usually occur spontaneously to some
degree, but not be highly exothermic.
Reaction Type Notes
• A solid product produced during a
chemical reaction in a solution is
called a precipitate.
• All double replacement reactions
produce either water, a precipitate, or
a gas.
Example: 2 NaI(aq) + Pb(NO3)2(aq)
PbI2(s) + 2NaNO3(aq)
Reaction Type Notes
• This table shows the steps to write
double replacement reactions.
Reaction Type Notes
 Most reactions which do
not appear to fit any of
these five patterns are
usually a combination of
two or more of them
happening simultaneously.
Reaction Type Notes
Practice Problem ANSWERS (page 291):
14. 2 Al(s) + 3 S(s)  Al2S3; synthesis
15. H2O(l) + N2O5(g)  2HNO3(aq);
synthesis
16. 4 NO2(g) + O2(g)  2N2O5(g);
synthesis and combustion
17. H2SO4(aq) + 2NAOH(aq)  Na2SO4
(aq) + 2H2O(l); synthesis
Reaction Type Notes
Practice Problem ANSWERS (page
292):
18. 2Al2O3(s)  4 Al(s) + 3O2(g)
19. Ni(OH)2(s)  NiO(s) +
2H2O(l)
20. 2 NaHCO3(s)  Na2CO3(aq) +
CO2(g) + H2O(l)
Reaction Type Notes
Textbook Practice (page 295):
 Problems #21-#24.
 Answer in your lab
composition journal.
Reaction Type Notes
Textbook Practice ANSWERS:
21. 2K(s) + ZnCl2(aq)  Zn(s) + 2KCl(aq)
22. No Reaction—Cl is below F in the
activity series
23. No Reaction—Fe is below Na in the
activity series
24. 2Al(s) + 3Pb(NO3)2(s)  3Pb(s) +
2Al(NO3)3(aq)
Reaction Type Notes
Textbook Practice (page 297):
 Problems #25-#27.
 Answer in your lab
composition journal.
Reaction Type Notes
Textbook Practice ANSWERS:
25. LiI(aq) + AgNO3(aq)  AgI(s) +
LiNO3(aq)
26. BaCl2(aq) + K2CO3(aq) 
BaCO3(s) + 2KCl(aq)
27. Na2C2O4(aq) + Pb(NO3)2(aq) 
PbC2O4(s) + 2NaNO3(aq)
Replacement Reactions (cont.)
• This table summarizes different
ways to predict the products of a
chemical reaction.
Reaction Type Notes
The following equation is what type of
reaction?
KCN(aq) + HBr(aq) → KBr(aq) + HCN(g)
A.
deconstructive
B.
synthesis
C.
single replacement
D.
double replacement
Reaction Type Notes
Which of the following is NOT one of
the four types of reactions?
A.
deconstructive
B.
synthesis
C. single replacement
D. double replacement