Reaction Types: Synthesis
In this type of reaction two substances join together to produce one,
more complex compound. These substances can be either elements or
simpler compounds.
Written using generic symbols, it is usually shown as:
A + B -- AB
These are some examples:
Mg + O2  MgO
H2 + O2  H2O
Fe + O2  Fe2O3
Notice that two elements are combining in each of these examples.
Rule: Synthesis reactions will occur between metals and nonmetals or
between two nonmetals. It will not occur between two metals:
e.g. Na + Ca  No Reaction (NR)
Synthesis can also occur between two compounds (or a compound and
an element) making a more complex compound.
examples:
CaO + CO2 
CaCO3
Na2O + CO2 
Na2CO3
KCl + O2 
KClO3
CaCl2 + O2 
Ca(ClO3)2
In summary, synthesis occurs between:
1) Two elements which form a binary compound.
2) Metal oxides and carbon dioxide to produce carbonates.
3) Chloride compounds and oxygen to produce chlorates.
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Reaction Types: Decomposition
During decomposition, one compound is broken apart into two(or more)
pieces. These pieces can be either elements or simpler compounds.
Written using generic symbols, it is usually shown as:
AB  A + B
Note: These are the reverse of synthesis reactions.
HgO 
H2O 
Fe2S3
Hg + O2
H2 +
O2
Fe + S
Rule: Decomposition reactions will occur as long as sufficient
energy is supplied. The energy will usually be in the form of
heat, electricity or light.
Notice that in every decomposition reaction, there is only one
substance on the left-hand (reactant) side. Don't forget that!!
Decomposition reactions may also split one compound into two
simpler compounds (or compound and an element) as in these
examples:
CaCO3 
CaO + CO2
Na2CO3  Na2O + CO2
KClO3 
KCl + O2
Ba(ClO3)2  BaCl2 + O2
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Here are three categories of decomposition reactions:
1) All binary compounds will break down into their elements.
2) All carbonates break down to a metal oxide and carbon
dioxide.
3. Chlorates will break down to a binary chloride compound
and oxygen.
Complete the following examples:
1) NaCl

2) NaClO3 
3) Li2S 3

4) Li2CO 
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Acids and Bases
Here are two other examples of Synthesis Reactions:
Metal oxides + water  bases.
CaO +
Na2O +
H2O  Ca(OH)2
H2O 
NaOH
Nonmetal oxides + water 
SO2 +
H2O 
N2O5 +
H 2O 
acids.
H2SO3
HNO3
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Reaction Types: Single Replacement
During single replacement, one element replaces another element in a
compound. There are two different possibilities:
1) One cation replaces another cation. Using generic symbols, it is
written as:
AB + X  XB + A
Element X has replaced A to form a new compound XB and the free
element A.
Remember that A and X are both cations (positively-charged ions) in
this example.
Rule: The element doing the replacing must be more active than the
element in the compound.
Some examples are:
Cu + AgNO3 
Ag +
Cu(NO3)2
Cu + Fe(NO3)2  NR (Cu is less active than Fe)
Zn +
HCl 
ZnCl2 +
H2
(demo)
Al +
CuCl2

AlCl3 +
Cu
(demo)
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The second possibility of replacement:
2) One anion replaces another. Written using generic symbols, it is:
AB + Y 
AY + B
Element Y has replaced B to form a new compound AY and the free
element B.
Remember that B and Y are both anions (negatively-charged ions) in
this example.
NaBr + Cl2 
KI +
Br2 
NaCl +
KBr +
Br2
I2
Once again, the element doing the replacing must be more active.
Notice: In a single replacement reaction, one reactant is always an
element. The other reactant is a compound.
Solve these examples:
1)
ZnS +
O2 
2)
KBr +
H2
3)
Ni +
4)
NaI
CoCl2 
+
Br2 
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Reaction Types: Double Replacement
During double replacement, the cations and anions of two different
compounds switch places.
Using generic symbols, it is written as:
AB + XY -- AY + XB
A and X are the cations in this example, with B and Y being the
anions.
Some examples are:
AgNO3 +
SrS +
KOH +
Na2SO4 
HCl 
Ag2SO4 +
SrCl2 +
H2SO4 
K2SO4 +
NaNO3
H2S(g)
H2O
Rule: In order for a double replacement reaction to occur, the reaction
must begin with soluble reactants that produce at least one of the
following three products:
an insoluble product (a precipitate)
a gas
water
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An equation that does not meet the above rule will result in no reaction
For example:
Cu(NO3)2(aq) + KClO3(aq)  Cu(ClO3)2(aq) +KNO3(aq)
Although the first requirement is met because both reactants are
soluble, both of the products are also soluble and neither is a gas or
water. Therefore, the reaction would not occur.
Cu(NO3)2(aq) +
KClO3(aq)  NR
Solve these examples:
1) NaNO3 + HgCl2 
2) Ca(OH)2 + HCl 
3) Al2(CO3)3 + H2SO4
4) Pb(NO3)2 + K2S 
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Reaction Types: Combustion
Combustion, in its most general sense, can mean the reaction of oxygen
gas (O2) with anything.
However, we will define combustion to mean the reaction of oxygen
with a compound containing carbon and hydrogen (hydrocarbon). A
common synonym for combustion is burn.
Written using generic symbols, it is usually shown as:
CxHy + O2  CO2 + H2O
These are some examples:
CH4 + O2 
CO2 +
H 2O
C2H6 + O2 
CO2 +
H 2O
C6H12O6 + O2 
CO2 +
H 2O
Notice that some compounds contain carbon, hydrogen AND oxygen.
However, the products are the same, in every reaction!
Reactions vary a bit when nitrogen (burns to form NO2) or sulfur
(burns to form SO2) are part of the formula.
C21H24N2O4 + O2  CO2 + H2O +
C2H5SH + O2  CO2 + H2O + SO2
NO2
Solve these sample combustions:
1)
2)
3)
C7H6O +
O2 
CH3COCH3 +
O2 
H2C2O4 +
O2 
A combustion reaction with insufficient oxygen yields carbon
monoxide (CO) rather than carbon dioxide (CO2). (A source of air
pollution)
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