A. Romero 2008
Three Types of Reaction Equations
CHEM 30A
1. The Formula Equation: All species in the equation are written as molecules or formula units.
This type of equation gives a useful overall picture of the reaction, with the species written as
they would appear on a reagent bottle.
2. The Complete (Total) Ionic Equation: All species in the equation are shown as they
predominantly exist in the reaction mixture (see Table 1 below). This type of equation is useful
as an actual representation of the species as they truly exist.
3. The Net Ionic Equation: Species are shown as they predominantly exist, like in the complete
ionic equation, however, any spectator ions are omitted. This type of equation is useful because
it only shows the species undergoing chemical change in the reaction.
Spectator Ion: Any ion that appears unchanged on both sides of the complete ionic equation.
Spectator ions are present in the reaction mixture, but do not participate in the chemical reaction.
Table 1. Forms of Species in Ionic Equations
Shown as Individual Ions
(species that ionize/dissociate completely)
soluble/aqueous ionic compounds
aqueous strong acids
aqueous strong bases
Shown as Molecules or Formula Units
(species do not ionize or only partially ionize)
insoluble/solid ionic compounds
aqueous weak acids
aqueous weak bases
most molecular compounds
In each of the examples below, the type of species is indicated under the formula equation, and any
spectator ions are circled in the complete ionic equation.
Example #1:
Formula Equation:
2 HClO4 (aq) + Mg(OH)2 (aq)  2 H2O (l) + Mg(ClO4)2 (aq)
strong acid
strong base
molecular
sol. ionic
Complete Ionic Equation:
2 H+ (aq) + 2 ClO4– (aq) + Mg2+ (aq) + 2 OH– (aq)  2 H2O (l) + Mg2+ (aq) + 2 ClO4– (aq)
Net Ionic Equation:
2 H+ (aq) + 2 OH– (aq)  2 H2O (l)
reduces to:
H+ (aq) + OH– (aq)  H2O (l)
Example #2:
Formula Equation:
2 HC2H3O2 (aq) + Ca(OH)2 (aq)  2 H2O (l) + Ca(C2H3O2)2 (aq)
weak acid
strong base
molecular
sol. ionic
Complete Ionic Equation:
2 HC2H3O2 (aq) + Ca2+ (aq) + 2 OH– (aq)  2 H2O (l) + Ca2+ (aq) + 2 C2H3O2– (aq)
Net Ionic Equation:
2 HC2H3O2 (aq) + 2 OH– (aq)  2 H2O (l) + 2 C2H3O2– (aq)
Example #3:
Formula Equation:
Pb(NO3)2 (aq) + 2 KCl (aq)  PbCl2 (s) + 2 KNO3 (aq)
sol. ionic
sol. ionic
insol. ionic
sol. ionic
Complete Ionic Equation:
Pb2+ (aq) + 2 NO3– (aq) + 2 K+ (aq) + 2 Cl– (aq)  PbCl2 (s) + 2 K+ (aq) + 2 NO3– (aq)
Net Ionic Equation:
Pb2+ (aq) + 2 Cl– (aq)  PbCl2 (s)
Example #4:
Formula Equation:
BaCl2 (aq) + Na2SO4 (aq)  BaSO4 (s) + 2 NaCl (aq)
sol. ionic
sol. ionic
insol. ionic sol. ionic
Complete Ionic Equation:
Ba2+ (aq) + 2 Cl– (aq) + 2 Na+ (aq) + SO42– (aq)  BaSO4 (s) + 2 Na+ (aq) + 2 Cl– (aq)
Net Ionic Equation:
Ba2+ (aq) + SO42– (aq)  BaSO4 (s)