Classifying Chemical Reactions
By classifying chemical reactions into several types, you can more easily predict what
products are likely to be formed.
1. Combustion reactions: oxygen combines with a substance and releases energy
Examples:
a)
CH4(g) +
2 O2(g) → CO2(g) +
carbon compound + oxygen → carbon dioxide
b) S(s)
+ O2(g) → SO2(g) +
(element + oxygen
→ compound +
2 H2O(g) + energy
energy
energy )
2. Synthesis reactions:
 synthesis means: to put together
 two reactants one product
Examples:
2 Mg(s) + O2(g) → 2 MgO(s)
2 Na(s) + Cl2(g) → 2 NaCl(s)
3. Decomposition:
 opposite of synthesis
 one reactant more than one product
 often require energy (endothermic)
∆
Example: CaCO3(s) → CaO(s) + CO2(g)
Special cases of decomposition:
∆
Carbonate → oxide + carbon dioxide
∆
hydroxide → oxide + water
4. Single Displacement: a single element reacts with a compound and displaces
another element from the compound.
Example: CuSO4 (aq) + Zn(s) → ZnSO4(aq) + Cu(s)
5. Double displacement: two solutions react to exchange ions to form new compounds.
Example: NaCl(aq) + AgNO3(aq) → NaNO3(aq) + AgCl(s)
Activity Series
Metals have similar physical properties but they are not equally reactive.
By making them react with water and/or acid it is possible to arrange them in
order of reactivity.
Activity Series: table that places some metals in order of reactivity starting with
the most reactive at the top.
K
Na
React with water
Ca
--------------------------Mg
Al
Zn
React with acid (MAZIT elements)
Fe
Sn
H --------------------------Cu
Ag
Unreactive ( don’t react with water nor acid)
Au
Pt


Metals above hydrogen will react with acids displacing hydrogen from it:
Example:
Mg(s)
+ HCl(aq) → MgCl2(aq) + H2(aq)
Cu(s)
+ HCl(aq) → no reaction
Displacement reactions in aqueous solutions: a more reactive metal will
displace a less reactive metal from a solution of its salt.
Example:
Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)

It is possible to confirm the activity series by using displacement reactions