Methane (CH4) is the smallest alkane (hydrocarbon with single bonds). Alkanes with four or fewer carbons exist as gases at room temperature and atmospheric pressure.
Alkanes have a variety of purposes, including fuel and industrial solvents.
Uses of Hydrocarbons
|Methane||Fuel in electrical generators; main component of natural gas|
|Ethane||Used in production of ethylene|
|Propane||Used in heating and cooking, such as propane grills|
|Butane||Lighter fluid and in some aerosols|
|Pentane||Solvent used in research and teaching labs and in production of polystyrene|
|Hexane||Component of glue used in shoes, leather products, and roofing|
|Heptane||A component of gasoline with a zero-octane rating|
|Octane||Gasoline additive (especially in the form of isooctane, 2,2,4-trimethylpentane)|
|Nonane||Component of diesel fuel|
|Decane||Component of jet fuel and diesel|
Ball-and-Stick Representations of Alkanes
As the number of carbons increases, so does the compound's boiling point. Furthermore, isomers with less branching have higher boiling points because these molecules are able to arrange themselves in closer proximity to neighboring molecules. The opposite is true for highly branched alkanes. Fractional distillation exploits the distinct boiling points of different alkanes by boiling a mixture of compounds and separating the components as they vaporize into gas. In crude oil, for example, the lighter, smaller hydrocarbons vaporize and are collected first, with the heavier components requiring additional heat to boil and vaporize.
Cycloalkanes, alkanes in cyclic form, generally have higher boiling and melting points than alkanes because their ring shape permits more surface interaction with surrounding molecules, resulting in stronger van der Waals forces.
Alkanes have low water solubility because the water molecules are polar and are attracted to each other (and not the nonpolar alkanes). The alkanes remain separate from the water molecules and are considered hydrophobic, or water repellant.When an alkane is present with oxygen and high temperatures, the alkane will burn into carbon dioxide and water in a combustion reaction. Smaller hydrocarbons are more volatile and ignite more easily, usually resulting in complete combustion and a blue flame. Larger molecules are less reactive because the van der Waals forces are stronger, and they require more heat to vaporize and mix with oxygen. Combustion of larger alkanes can result in incomplete combustion, giving a yellow flame with black smoke, creating a mix of carbon dioxide and carbon monoxide.