Predicting the Products of a Chemical Reaction
•The number of elements and/or compounds reacting is a good indicator of possible reaction
type and thus possible products.
1. Combination Reactions (Synthesis)
General Equation: A + B  AB
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Reactants: Generally two elements, or two compounds (where at least one compound is
a molecular compound).
Probable Products: A Single Compound.
Example: Burning Magnesium in air:
2 Mg + O2  2 MgO
2. Decomposition Reactions
General Equation: AB  A + B
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Reactants: Generally a single binary compound or a compound with a polyatomic ion.
Probable Products: Two elements (for a binary compound), or two or more elements
and/or compounds (for a compound with a polyatomic ion).
Example: Aluminum chloride is strongly heated: 2AlCl3  2Al + 3Cl2
When there is a polyatomic ion involved in the reactant, look up the rules in your
Chemistry Reference Table.
Ex. Potassium chlorate is strongly heated: KClO3  KCl + 3O2
3. Single-Replacement Reactions
Metal replaces metal general equation: A + BC  AC + B
Halogen replaces halogen general equation: C + AD  AC + B
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Reactants: An element and a compound. In a single-replacement reaction, an element
replaces another element from a compound in aqueous solution. For a singlereplacement reaction to occur, the element that is displaced must be less active than
the element that is doing the displacing.
Probable Products: A different element and a new compound.
Example:
Potassium dropped in an aluminum chloride solution:
3K + AlCl3  3KCl + Al
4. Double Replacement Reactions
General Equation: AB + CD  AD + CB
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Reactants: Two ionic compounds. In a double-replacement reaction, two ionic
compounds react by exchanging cations to form two different compounds.
Probable Products: Two new compounds. Double-Replacement reactions are driven by
the formation of a precipitate, a gaseous product, or water.
Example:
Mix aqueous solutions of barium chloride and potassium carbonate:
BaCl2 + K2CO3  BaCO3 + 2KCl
5. Combustion Reactions
Equation: CxHy + O2  CO2 + H20
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Reactants: Oxygen and a compound of C, H, (O). When oxygen reacts with an element or
compound, combustion may occur.
Products: CO2 and H2O.
Example:
The combustion of propane (C3H8) gas in air:
C3H8 + 5O2  3CO2 + 4H2O
6. Net Ionic Equations for Double Replacement Reactions
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Many important chemical reactions take place in water, aqueous solution
Ex. The aqueous solutions of silver nitrate with sodium chloride produces silver chloride
and aqueous sodium nitrate (double replacement reaction)
This standard method of writing equations does not show that like most ionic
compounds, the reactants and one of the products separate into cations and anions
when they dissolve in water
Complete ionic Equation – an equation that shows dissolved ionic compounds as
dissociated free ions
Ag+ + NO3- + Na+ + Cl-  AgCl + Na+ + NO3-
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Ions that remain unchanged throughout the entire chemical reaction, and are the same
in the product as they are in the reactants are not required in the equation
Spectator ion – an ion that appears on both sides on an equation and is not directly
involved in the reaction. Na+ and NO3- are not directly involved in the reaction
Net ionic equation – an equation for a reaction in solution that shows only those
particles that are directly involved in the chemical change
Ag+ + Cl-  AgCl
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When removing the unnecessary ions to make a net ionic equation, one must make sure
that the charge of the equation remains balanced
A net ionic equation shows only those particles involved in the reaction and is balanced
with respect to both mass and charge