Chemical Reactions
Part 1: Decomposition and
Synthesis Reactions
Objectives
• -To identify decomposition and
synthesis chemical reactions
• -To predict the products of these
two types of reactions
2
Symbols in Equations
• The arrow (→) separates the reactants from
the products
• (s) = solid:
Fe(s)
• (g) = gas:
CO2(g)
• (l) = liquid:
H2O(l)
Symbols in Equations
•
double arrow indicates a
reversible reaction (more later)
heat
• 
 ,    heat is supplied
to the reaction
•
a catalyst is supplied (i.e.
Pt
platinum)
 
Classifying and Predicting
Chemical Reactions
• Oxidation-Reduction reactions - electrons
are transferred from one atom to another
• There are 5 classifications:
– Decomposition
– Synthesis
– Combustion
– Single displacement
– Double displacement (ionic)
5
Decomposition Reactions
• Decompose = fall apart
• Decomposition reactions- one
compound decomposes into two or
more elements or compounds
• Key: only 1 reactant
• Usually involves energy or heat
6
Decomposition
• Binary compounds (two elements) will split
into those two elements:
AB  A + B
• Tertiary compounds (three elements) will
have one element in BOTH products
ABC  AB + BC
7
Decomposition Reactions
A. Electrolysis (adding electricity) of
compounds produces the elements
2 H2O  2 H2 + O2
2 NaCl  2 Na + Cl2
8
Decomposition Reactions
B. Metallic (any positive ion) chlorates
decompose into metallic chlorides and
oxygen when heated
2 KClO3  2 KCl + 3 O2
C.
Metallic carbonates decompose into
metallic oxides and carbon dioxide when
heated
CaCO3  CaO + CO2
9
Decomposition Reactions
D. Hydrated compounds yield the
anhydrous compound and water when
heated
CuSO4  5 H2O  CuSO4 + 5 H2O
E.
Oxides of the less active metals (see
activity series) form the metal and
oxygen when heated
2 HgO  2 Hg + O2
10
Decomposition Reactions
F.
Acids (hydrogen with negative ion)
decompose into water and nonmetallic
oxides
H2CO3  H2O + CO2
2 H3PO4  P2O5 + 3 H2O
G. Bases (metallic hydroxides) decompose
into water and metallic oxides
Ca(OH)2  CaO + H2O
11
Decomposition Reactions
H. Peroxides decompose into oxides and
oxygen.
2 K2O2  2 K2O + O2
2 H2O2  2 H2O + O2
water is the oxide of hydrogen
12
Synthesis Reactions
• Synthesize = to make or put together
• Synthesis reactions-two or more
elements or compounds unite to form
one product
• Key: 2 elements OR two compounds when
both are oxides with only one product
13
Synthesis Reactions
A. Oxygen combines with most elements to
form oxides
2 Mg + O2  2 MgO
C + O2  CO2
B.
Metallic elements + nonmetallic
elements yield ionic compounds (ionic
compounds called salts)
2 Al + 3 Cl2  2 AlCl3
2 K + I2  2 KI
14
Synthesis Reactions
C. Nonmetallic elements tend to combine
with each other to form covalent (molecular)
compounds
S8 + 8 F2  8 SF2
P4 + 6 Cl2  4 PCl3
15
Synthesis Reactions
D. Oxides of metals + water form bases
(metallic hydroxides) Water is an oxide!
CaO + H2O  Ca(OH)2
Na2O + H2O  2 NaOH
16
Synthesis Reactions
E.
Oxides of nonmetals + water form
acids- acids usually made from an “ate”
ion
P2O5 + 3 H2O  2 H3PO4
SO3 + H2O  H2SO4
F.
Oxides of metals + oxides of nonmetals
yield ionic compounds- usually contain an
“ate” ion
17
Na2O + SO3  Na2SO4
Objectives
• -To identify decomposition and
synthesis chemical reactions
• -To predict the products of these
two types of reactions
18