Reaction Prediction
There were five basic types of chemical reactions that we
learned in chemistry I.
**** Please remember that all products must have their formulas written by
crossing and reducing the charges. The subscripts DO NOT SIMPLY MOVE
FROM LEFT TO RIGHT.
**** Also, all reactions must be balanced after the products are predicted.
1.
Synthesis reaction: occurs when two or more simple substances
(elements or compounds) are combined to form one new and more
complex substance. The general form of a synthesis reaction is
element + element  compound
Fe + S  FeS
2.
One important note: the elements must have opposite charge in order to
react. If you have two metals trying to react, they will not react and we
will write NO RXN. If we have two non-metal elements, they will not
react and we will write NO RXN.
Single replacement reaction: occurs when one element displaces
another in a compound. The general form of a single displacement
reaction is
element + compound  element + compound
M +AB  A + MB (M is metallic element) – SR-M
Or
N+ AB  B + AN (N is a nonmetallic element) SR-N
3.
Zn + 2HCl  H2 + ZnCl2 SR-M
O2 + 2 NaCl  Cl2 + 2 Na2O SR - M
Double replacement reaction (metathesis): occurs when the cation (+)
and the anion (-) of the two reactants are interchanged. The general
form of a double displacement reaction is
compound (AB) + compound (CD)  compound (AD) + compound(CB)
FeS +2HCl  FeCl2 + H2S
4.
Decomposition reaction: occurs when energy in the form of heat, light,
electricity, or mechanical shock is supplied. A compound may
decompose to form simpler compounds and/or elements. The general
form of a decomposition reaction is
compound  two or more substances
There are six general types of decomposition reactions
A
b.
c.
Most compounds can be decomposed by electricity or heat into their
elements.
2NaCl  2Na + Cl2
Metallic carbonates, when heated, decompose to form the metal
oxide and carbon dioxide.
Li2CO3  Li2O + CO2
General form: Metal carbonate  Metal oxide + CO2
Metallic chlorates, when heated, decompose to form metal chloride
and oxygen gas.
General form:
5.
2KClO3  2KCl + 3O2
Metal chlorate  Metal chloride + O2
Combustion reactions -- Combustion reactions are simply the
burning of organic hydrocarbons. They involve a hydrocarbon ( a
compound that begins with CH) and oxygen reactiong to form
carbon dioxide and water.
C3H8 + 5 O2  3 CO2 + 4 H2O
General form:
CxHy + O2  CO2 + H2O
The trick to balancing these equations is to make the number of
hydrogen atoms a multiple of 4 by changing the coefficient of the
hydrocarbon.
In addition to these five basic types we have some other types of reactions that we have not yet covered.
A. Lewis Acid Base reactions
These involve a lewis acid reacting with a lewis base. The acid will be a column 13 halide compound like
BF3 that is electron poor (Lewis acid) because it has only 6 valence electrons instead of the full octet that
leads to the maximum stability. The base will be a column 15 halide or ammonia (NH3) that is electron
rich (Lewis base) because of the lone pair. Basically, the two chemicals smoosh together (so I call it a
SMOOSH reaction).
EXAMPLES:
BCl3 + NH3  BCl3NH3
BI3 + PCl3  BI3PCl3
B. Complex ion formation
Complex ions are formed when a large excess of a ligand is added to a transition metal (usually).