|MadSci Network: Chemistry|
Although both methane and isooctane are made up of the same elements - C, H, and O - their respective molecular weights are very different. Methane has a molecular weight of 16 (molecular formula = CH4). Iso-octane has a molecular weight of 114 (molecular formula = C8H18). The boiling point is generally roughly proportional to the molecular weight of an organic compound. Since the molecular weight of iso-octane is much higher than that of methane, it's boiling point is much higher as well.
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