The main tasks of Chap 8
Sect 1 - Writing reactions from word
problems – challenging
Sect 2 - Balance Equations—easiest
Sect 3 - Classify Equations, Complete
Equations—challenging
Sect 4 – Write Net Ionic equations
Classifying Reactions
You will learn to recognize the
different types of reactions AND
How to complete products (predict).
Combustion Reactions
“Burning”
• Oxygen is a reactant.
• Energy is produced
Combustion of carbon compounds yield carbon
dioxide(CO2) and water (H2O ).
• Mg + O2  MgO
• CH4 + O2  CO2 + H2O
Synthesis Reactions
Two or more elements or compounds
combine to form ONE PRODUCT.
• Mg + O2  MgO
• H2 + O2  H2O
• SO 3 ( g )  H 2 O ( l )  H 2 SO 4 ( aq )
Decomposition Reactions
ONE REACTANT (compound) breaks into
elements or smaller compounds.
• H2O  H2 + O2
• MgO  Mg + O2
Displacement Reactions
• Also called Replacement reactions
• Single Displacement/Replacement
– Use the Activity series
• Double Displacement/Replacement
– Precipitation Reactions
• Use the Solubility Rules
– Acid Base Reactions
Single Displacement
Part of an ionic compound is removed and replaced by
a new element.
• ELEMENT + COMPOUND  COMPOUND + ELEMENT
There are 2 subtypes of single replacement reactions.
- Cationic replacement
- Anionic replacement
Single Displacement subtype
CATIONIC REPLACEMENT:
• If the Element is a Metal, it replaces the
metal in the compound.
• Cu + AgNO3  Cu(NO3)2 + Ag
Single Displacement subtype:
ANIONIC REPLACEMENT:
• If the Element is a Non-metal, it replaces the
non-metal in the compound.
• Cl2 + NaBr  NaCl + Br2
Single Replacement Rxns
• To determine if a Single Replacement Reaction
really happens, use the ACTIVITY SERIES
reference sheet.
• If an element is higher on the chart, it will
become a compound.
• If the higher element is already in a
compound, then NO reaction occurs
Double Replacement Rxns
• Two Ionic Compounds that exchange
partners.
• XY + AB  AY + XB
• Only Positive with Negative
• Positive Ion listed first
Double Replacement Rxns
• To determine if the reaction occurs, use the
SOLUBILITY RULES.
• A reaction occurs if a solid or water forms
when two aqueous solutions of ionic
compounds are mixed.
• If the products are both aqueous ionic
compounds, then no reaction occurs.
Solubility Rules info.
• Soluble = dissolves in water = (aq) =
clear
• Insoluble= doesn’t dissolve in water =
SOLID = (s) = cloudy = precipitate = ppt
Section 4: Net Ionic Equations
• Three ways to write the same equation
(usually with double replacement rxns):
• 1. Complete Molecular Equation
• 2. Complete Ionic Equation
• 3. Net Ionic Equation
Dissolving (aq) separates
the ions
•
•
•
•
NaCl (s) in water NaCl (aq)
NaCl (aq) means Na+(aq) + Cl- (aq)
The Ions move separately in solution.
In some equations we separate the ions and
write the charges.
Complete Molecular Eqn
• This is what we have been doing. Write the
compounds with the ions together.
• Example: NaCl (aq) + AgNO3 (aq)
AgCl (s) + NaNO3(aq)
Complete Ionic Eqns
• Write the aqueous compounds as separate
ions. Be sure to put the CHARGES ON THE
IONS!
• Keep the solid(insoluble) or water molecules
together.
• Example:
+
Na (aq) + Cl (aq) + Ag+(aq) + NO3 (aq)

AgCl (s) + Na+(aq)+ NO3-(aq)
Net Ionic Equations
• Take the Complete ionic equation and remove
any ion that is aqueous on both sides.
These ions are called Spectator Ions.
OR
• Find the Solid product or water, keep that part
AND keep the reactant ions that made the solid or
water.
• Ex: Ag+ (aq) + Cl- (aq)  AgCl(s)
Net Ionic Eqns with Acids and Bases(
H+ and OH-)
When acids (HA) and Bases (ZOH) mix, the H+
and OH- combine to become H2O(l).
This is called a neutralization reaction.
The water H2O(l) stays together like insoluble
solids. So you keep it in the Net Ionic
equation.
Ex. H+ + OH-  H2O
Example: Complete and Net
Ionic Equations page 1
Cu(NO3 )2 (aq) + NaOH(aq)  ????
1) Write Complete Molecular Equation:
Cu(NO3 )2 (aq) + NaOH(aq)  Cu(OH)2 (s) + NaNO3 (aq)
2) Write Complete Ionic Equation: [separate all (aq),
put charges on ions; keep solids together.]
Cu+2(aq) +2NO3 -1(aq) + 2Na+1 (aq) + OH-1 (aq)
 Cu(OH)2 (s) + 2Na+1 (aq) +
And then…
2NO3 -1 (aq)
Example: Complete and Net
Equations page 2
Ionic
3) Write Net Ionic Equation: [eliminate spectator
ions, keep ions that make solid, keep solids.]
Cu+2(aq)
+ OH-1 (aq)  Cu(OH)2 (s)