Types of Chemical Reactions
(3.2) Combustion Reactions
The Fire Triangle
• for a combustion reaction to occur, 3
things must be present:
1. Fuel
2. Oxygen
3. Heat
• a hydrocarbon is a compound that is
composed only of the elements carbon and
hydrogen
• ex: methane gas CH4(g)
• combustion of a hydrocarbon always
produces the compounds, carbon dioxide and
water.
• ex: CH4(g) + 2 O2(g)  CO2(g) + 2 H2O(g)
Hydrocarbons
• A general formula for a hydrocarbon is CxHy
• Hydrocarbons are often used as fuels
• Examples
Name
Formula
methane
CH4(g)
propane
C3H8(g)
butane
C4H10(g)
acetylene
C2H2(g)
Combustion Reactions
• Combustion of hydrocarbons can be complete
or incomplete.
• the products depend on the amount of O2
present
Complete Combustion
• occurs when a sufficient amount of O2 is
present
• all the C atoms and H atoms react to form CO2
and H2O
• In general:
hydrocarbon + oxygen  carbon dioxide + water
CxHy + O2(g)  CO2(g) + H2O(g)
Incomplete Combustion
• occurs if there is not a sufficient amount of O2
– ie. fuel is not completely converted into carbon dioxide
and water
• products include H2O as well as any combination of
the following:
– CO
–C
– CO2
• examples:
2 CH4(g) + 3 O2(g)  2 CO(g) + 4 H2O(g)
2C3H8(g)+ 7O2(g)  2C(s) + 2CO(g) + 2CO2(g) + 8H2O(g)