5.1 The Combustion of Hydrocarbons

Background Organic Compound: a molecular compound containing one or more carbon-carbon bonds

These impurities cause air pollution Many fuels contain impurities such as sulfur compounds and heavy metals. These impurities cause air pollution The burning of hydrocarbons is a large contributing factor to the release of carbon dioxide into the atmosphere. Carbon dioxide is one green house gas that contributes to the theory* of global warming. *reminder that scientific theory =/= everyday theory

Combustion Reaction Requires the presence of oxygen for complete combustion The reactants are any material and oxygen The general equation for a complete combustion reaction of a hydrocarbon is: Hydrocarbon + oxygen → carbon dioxide + water C3H8 (g) + O2 (g) → CO2 (g) + H2O (g) C3H8 (g) + 5O2 (g) → 3CO2 (g) + 4H2O (g)

The general equation for a combustion reaction of an element is: compound + oxygen → oxides of the compound S8 (g) + 8O2 (g) → 8SO2 (g)

Incomplete Combustion Combustion of a hydrocarbon occurs when the supply of oxygen is limited. It is said to be “fuel rich” Flames from incomplete combustion are often yellow, sooty and considerably cooler than flames from complete combustion. They produce a wider range of products and are generally represented by more than one chemical equation

Incomplete combustion of Heptane C7H16 (g) + 7O2 (g) → 3C(s) + 2CO (g)+ 2CO2 (g)+ 8H2O (g) + energy C7H16 (g) + 11O2 (g) → 14CO (g)+ 2CO2 (g)+ 8H2O (g) + energy

Fire Fighting We can stop combustion reactions in several ways. Fire requires oxygen, heat and a fuel source to continue to burn. Attacking any of these factors can reduce or stop a fire. Water: Water serves to cool down a fire, absorbing some of the heat from a combustion reaction. Smothering: Using a blanket overtop or otherwise reducing the oxygen intake, will limit the fire’s ability to burn (complete->incomplete->no combustion)

Fire Extinguishers: There are different kinds of fire extinguishers developed for the variety of fires that exist (combustible liquid, electrical, etc) 3 general types: - Water: They propel water to cool the fire. - Dry Chemical: These serve to cut off the fuel source from oxygen by covering it in a fine powder. - CO2: These propel liquid CO2 that expands into a snowy foam. It smothers the fire and absorbs heat from the fire as it evaporates into a gas.

Using page 194-195 address the concerns related to incomplete combustion