Some
Simple
Patterns of
Chemical
Reactivity
Synthesis
• A chemical change in which two or more
substances react to form a single new
substance.
A + B AB
• A.K.A. (Combination)
Decomposition
Examples:
•
Formation of metal oxides
Ca (s) + O2 (g) CaO(s)
•
A chemical change in which a single compound
breaks down into two or more simpler products
Usually requires energy in the form of heat light
or electricity.
AB A + B
•Formation of non metal oxides
S(s) + O2 (g) SO2(s)
2S(s) + 3O2 (g) SO3(s)
•Formation of metal and non-metal halides
2C(s) + 3F2(g) 2CF3(s)
Single Displacement
Examples:
•
•Electrolysis
2H2O
−
e
→
2H2 (g) + O2 (g)
•
A chemical change in which one element
replaces a second element in a compound.
Can be predicted from the activity of species
involved.
A + BX AX + B
•Decomposition of polyatomic compounds
2KClO3 (s)
∆

→
2KCl (s) + 3O2 (g)
Activity Series of Metals
Examples:
The activity series to the left can be used to
predict the occurrence of single replacement
reactions.
• A metal in this series will replace any metal
below it in the series.
• Although hydrogen is not a metal, it is included
in this series because it can be replaced by the
metals above it in the series.
• For example, zinc can displace lead from a lead
compound in solution by can not displace
sodium from a sodium compound.
• Halogen replacement reactions are predicted
from the reactivity of group 7 elements which
decrease in reactivity down the group.
Hydrogen replacement
Na(s) + H2S(aq) Na2S(aq) + H2(g)
•Halogen replacement
Br2(l) + 2KI(aq) 2KBr(aq) + I2(g)
•Metal replacement
Cu(s) + AgNO3(aq) Cu(NO3)2(aq) + Ag(s)
Double Displacement
Practice:
Write a single replacement reaction for each
of the following below, then determine if the
reaction should occur based on the activity of
the species.
•
•
A chemical change involving an exchange of
positive ions between two compounds.
Generally takes place in aqueous solution and
often produces a precipitate, gas or molecule.
AX + BY AY + BX
1. Lead added to magnesium chloride
2. Calcium added to water
3. Iron added to silver nitrate
4. Chlorine is added to potassium iodide
5. Copper added to water
Examples:
Combustion
•
Formation of a precipitate
2KI(aq) + Pb(NO3)2(aq) 2KNO3 (aq) + PbI2(s)
•Production of a gas
2NaCN(aq) + H2SO4(aq) 2HCN(g) + Na2SO4(aq)
•Neutralization
HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)
•
A chemical change in which an element or
compound reacts with oxygen to produce
oxides of all elements reacting.
Often produces energy in the form of heat and
light.
You Decide!
What type of reaction is it?
1) NaOH + KNO3 NaNO3 + KOH
2) CH4 + 2 O2 CO2 + 2 H2O
3) 2 Fe + 6 NaBr 2 FeBr3 + 6 Na
4) CaSO4 + Mg(OH)2 Ca(OH)2 + MgSO4
5) NH4OH + HBr H2O + NH4Br
6) Pb + O2 PbO2
7) Na2CO3 Na2O + CO2