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1
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- There are 6 classifications of reactions:
- Combustion
- Oxidation-reduction
- Synthesis
- Decomposition
- Single displacement
- Double displacement
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2
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- Reactions that involve the dissociation of ions are called ionic
reactions.
- Most of these are a double displacement type.
- These reactions take place in water but the water does not take part in
the reaction. Water is the medium
of occurrence
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3
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- Reactions are written with molecular formulas.
- CaCl2(aq)+K2SO4(aq)àCaSO4(s)+ 2KCl(aq)
- From molecular formulas the
reacting species can be written as complete ionic equations.
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4
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- Complete ionic equations are written to show the dissociated state of
the compound:
- Ca+2(aq) +2Cl-(aq) +
2K+(aq)+SO4-2(aq)
àCaSO4(s)+2K+(aq)
+2Cl-(aq)
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5
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- The physical states are included as subscripts. The symbol (aq) means that the
compound is not only dissolved in water but the ions are already
separated in solution.
- Formulas for insoluble compounds are not separated. The ions of water insoluble compounds
are immobile (CaSO4)
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6
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- The equations must be balanced for number of atoms and charge.
- The equation must be electrically neutral.
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7
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- Net ionic equations are written to express only the ions involved in
forming the precipitate.
- If an ion appears on both sides of the equation but does not take part
in forming the precipitate, it is called a spectator and is cancelled
from the equation.
- Be sure cancelled species are in the same physical state
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8
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- When all the spectator ions are cancelled, the remaining ions and the
precipitate are written as the net ionic equation.
- Ca+2(aq) +2Cl-(aq)
+ 2K+(aq)+SO4-2(aq)
àCaSO4(s)+2K+(aq)
+2Cl-(aq)
- Net Ionic Equation:
- Ca+2(aq) + SO4-2(aq)
à CaSO4(s)
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Notes