Classifying Chemical Reactions
Important Terms:
Acid: An acid is a compound that starts with hydrogen (H+). Example: H2SO4, HCl
Base: A base is a compound that ends with a hydroxide ion (OH-). Example: NaOH
Salts: An ionic compound. Example: NaBr
Acidic Oxide: A nonmetal combined with oxygen. Also know as a nonmetal oxide. Example: CO2 or P4O10
Basic Oxide: A metal combined with oxygen. Also known as a metal oxide. Example: Na2O, SrO, or Al2O3
Synthesis Reactions
A synthesis reaction is a chemical reaction in which two or more substances react or COMBINE to produce a SINGLE product. When two
elements react, the reaction is always a synthesis reaction.
A + B  AB
There are four types of synthesis reactions. It is important to identify these types of synthesis reactions in order to accurately predict the
products.
Type
Element + Element 
Acidic Oxide + Basic
Acidic Oxide + Water 
Basic Oxide + Water 
Compound
Oxide  Salt
Acid
Metal Hydroxide (Base)
Description
Two or more substances
A non-metal oxide and
A non-metal oxide
A metal oxide combines
combine to produce a new
metal oxide react to
combines with water to
with water to form a
+
compound.
produce an ionic
form an acid (H
base (metal combined
**Balance the charges of the compound.
compound).
with OH-).
ions in the products.
** Balance the charge on
**Balance the charge on
H+ with the attached
the metal with the OHcompound.
ion.
Example
N2(g) + 3H2(g)  2NH3(g)
SO3 + BaO  BaSO4
CO2(g) + H2O(l) 
MgO(s) + H2O(l) 
H2CO3(aq)
Mg(OH)2(s)
2Fe(s) + 3Cl2(g)  2FeCl3(s)
Li2O(s) + CO2(g) 
Li2CO3(s)
SO3 + H2O(l)  H2SO4
BaO + H2O(l) 
Ba(OH)2
Element + Element  Compound:
4Al + O2  2Al2O3
2Mg + O2  2MgO
Acidic Oxide + Basic Oxide  Salt Practice:
CO2 + CaO  CaCO3
SO3 + Li2O  Li2SO4
Acidic Oxide + Water  Acid:
SO3 + H2O(l)  H2SO4
Basic Oxide + Water  Metal Hydroxide (Base):
Li2O + H2O(l)  2LiOH
Al2O3 + 3H2O(l)  2Al(OH)3
Cu2O + H2O(l)  2CuOH
CuO + H2O(l)  Cu(OH)2
Decomposition Reactions
The reverse of synthesis reactions, a decomposition reaction is one in which a single compound breaks down into two or more elements or
new compounds. This is usually due to the addition of heat, light, or electricity. In generic terms, decomposition reactions look like the
following:
AB  A + B
Type
Compound  Element +
Decomposition of salts
Decomposition of Acids Decomposition of Bases
Element
Description
A compound decomposes
Several salts can be
Acids can be
Most bases decompose
into two different elements.
decomposed to form a basic
decomposed into water
to form water and a
** Remember diatomic
oxide and an acidic oxide.
and acidic oxide.
basic oxide.
elements occur in twos.
Example
2HgO(s)  2Hg(l) + O2(g)
Carbonates
H2SO4(aq)  H2O(l) +
Ca(OH)2(s)  H2O(l) +
CaCO3(s)  CaO(s) + CO2(g) SO3(g)
CaO(s)
Sulfates
ZnSO4(s)  ZnO(s) + SO3(g)
Chlorates
2KClO3(s)  2KCl(s) + 3O2(g)
** A hydrate decomposes into the compound and water.
Practice:
o 2NaClO3 2NaCl + 3O2
o 2AgI  2Ag + I2
o Cs2CO3 Cs2O + CO2
o Ni(ClO3)2 NiCl2 + 3O2
o Ni(OH)2 H2O + NiO
o 2AlF3 2Al + 3F2
COMPLETE QUESTION 3 ON BALANCING EQUATION SHEET AND IDENTIFY AS A SYNTHESIS OR DECOMPOSITION
EQUATION. IF SYNTHESIS, IDENTIFY THE TYPE.
Combustion Reactions
In a combustion reaction, oxygen combines with a substance and releases energy in the form of heat and light. A combustion reaction will be
in the form:
FUEL + O2(g) Common Oxide of the fuel
 If the fuel contains … then a product is…
o C  CO2
o H  H2O
o N  NO2
o S  SO2
 ALSO:
CwHxOySz + O2(g)  CO2(g) + H2O(g)
**A combustion reaction needs oxygen gas O2(g) and a fuel!!!**
Example:
C3H8 (s) + O2(g)  3CO2(g) + 4H2O(g)
a)
b)
c)
d)
e)
Practice:
Complete the combustion reactions for the following organic molecules.
C2H6
f) C2H6O
C3H8
g) C6H8O6
C3H6O3
h) C2H4O2
C13H28
i) C22H46
C2H6O2
j) C36H74
k)
l)
m)
n)
o)
C8H20
C5H10O5
C20H30O
CH4O
C4H8O4
Replacement Reactions
In contrast to synthesis, combustion, and decomposition reactions, many chemical reactions involve the
replacement of an element in a compound. There are two types of replacement reactions: singlereplacement and double-replacement.
Single Replacement Reactions
Single - replacement reactions are those in which the atoms of one element replace the atoms of another
element in a compound. Something is passes from one group to another much like someone cutting in
on a dance. The person who was initially standing alone is now dancing in a partnership while someone
who had been dancing is now by themselves. This is the form of
A + BX  AX + B
Type
Metal + water
Metal + Ionic Compound
Description
A metal and water react
and the metal replaces a
hydrogen atom in a
water molecule.
A metal and an ionic
compound react and the
metal will replace the metal
in the compound.
Example
2Li (s) + 2H2O(l) 
2LiOH(aq) + H2(g)
Cu(s) + 2 AgNO3(aq) 
2Ag(s) + Cu(NO3)2
Non-metal + Ionic
Compound
A non-metal and an
ionic compound will
react and the non-metal
will replace the nonmetal in the compound.
Halogens are frequently
involved in these
reactions.
F2(g) + 2 NaBr(aq) 
2NaF(aq) + Br2(l)
Metal atoms might replace another metal, depending on their
reactivities. A metal’s reactivity is its ability to react with
another substance. This activity series orders metals by their
reactivity with other metals. The activity series table will help
up predict whether a chemical reaction will occur or not.
Cu(s) + 2 AgNO3(aq)  2Ag(s) + Cu(NO3)2
Single – replacement reactions like the one between copper
and aqueous silver nitrate determines a metal’s position on the
list. The most active metals, which are those that do replace
the metal in a compound, are at the top of the list. The least
active metals are at the bottom.
**A specific metal cannot replace any metal listed above it.
For example, copper atoms replace silver atoms in a solution
of silver nitrate. However, if you place a silver wire in
aqueous copper(II) nitrate, the silver atoms will not replace
the copper. Silver is listed below copper in the activity series
and no reaction occurs. The letters NR (no reaction) are
commonly used to indicate that a reaction will not occur.
Ag(s) +Cu(NO3)2(aq)  NR
Similar to metals, halogens exhibit different activity levels in single – replacement reactions. A more
reactive halogen replaces a less reactive halogen that is part of a compound dissolved in water.
Br2(g) + 2NaF(aq)  NR
Practice:
Fe(s) + CuSO4(aq)  FeSO4(aq) + Cu(s)
Br2(l) + MgCl2(aq)  NR
6H2O(l) + 2Al(s) 3H2(g) + 2Al(OH)3(s)
3Mg(s) + 2AlCl3(aq)  3MgCl2(aq) + 2Al(s)
2K(s) + ZnCl2(aq) 2KCl(aq) + Zn(s)
Cl2(g) + HF(aq)  NR
Fe(s) + Na3PO4(aq) NR
Double – Replacement Reactions
A double-replacement reaction involves an exchange of ions between two compounds. Thinking back to the
dance analogy, two couples dancing together when they decide to switch partner with one another.
AX + BY  AY + BX
In this generic equation, A and B represent positively charged ions (cations), and X and Y represent negatively
charged ions (anions). You can see that the anions have switched places and are now bonded to the other cations
in the reaction. In other words, X replaces Y and Y replaces X.
Step
1.
2.
3.
4.
5.
6.
7.
Guidelines for Double-Replacement Reactions
Example
Write the components of the reactants in a
Ca(OH)2(aq) + HCl(aq)
skeleton equation.
Identify the cations and anions in each
Ca(OH)2 has Ca2+ and OHcompound.
HCl has H+ and ClPair up each cation with the anion from the Ca2+ pairs with Clother compound.
H+ and OHWrite the formulas for the products using
CaCl2
the pairs from step 3.
H2O
Write the complete equation for the double- Ca(OH)2(aq) + HCl(aq)  CaCl2 + H2O
replacement reaction.
Use the solubility chart to predict the states Ca(OH)2(aq) + HCl(aq)  CaCl2(aq) + H2O(l)
of the products.
Balance the equation.
Ca(OH)2(aq) + 2HCl(aq)  CaCl2(aq) + 2H2O(l)
**Note: A solid produced during a chemical reaction in a solution is called a precipitate.
Example: 2NaOH(aq) + CuCl2(aq)  2NaCl(aq) + Cu(OH)2(s)