Fractional Ditillation & Hydrocarbon Propeties
Fractional distillation is the breaking up of crude oil into different hydrocarbon fractions. Crude oil is made up of lots of a mixture of different hydrocarbons. Crude oil heated --> Use of a fractionating column which has a temperature gradient (cold at the top and hot at the bottom) --> Fractions containg mixtures of hydrocarbons are obtained. --> Fractions contain many substances with similar boiling points. --> Fractions with a low boiling point exit from the top of the fractionating column. --> Therefore fractions with a low boiling point exit from the bottom. Extraction of crude oil is a major pollution cause. Higher Level - Covalent bonds between carbon and hydrogen atoms within a hydrocarbon molecule are stronger than the intermolecular forces between hydrocarbon molecules. During boiling intermolecular forces are broken. Intermolecular forces between larger hydrocarbon molecules are stronger than those between smaller ones. Hydrocarbons with large molecules have a higher boiling temperature than those with smaller molecules.
Cracking is breaking down large hyrocrbons and making them into shorter, more useful hydrocarbons. We do this because it means using up less crude oil which means there is more for other stuff. We also do this so that the political demands are kept and the oil isn't wasted. Crude oil is finite which means that it can run out and it will take millions of years to remake some.