Chapter 12 - Alkanes Flashcards
What are alkanes?
Alkanes are the main constituent of crude oil, and saturated hydrocarbons (compounds which only contain carbon and hydrogen)
What is fractional distillation of crude oil?
Crude oil, or mixtures like petroleum, are heated and the majority of the substances boil and begin to rise up the fractionating column, cooling down as they do so. As they cool down the larger molecules begin to condense and then can be extracted from that fraction whilst the shorter molecules are still gaseous and continue to rise up the column, until they too condense
What is cracking of alkanes?
Cracking alkanes is where the C - C bond in alkanes is broken down and forms two new hydrocarbon molecules
How does thermal cracking work?
It happens at high temperatures and pressure, resulting in large numbers of alkenes
How is catalytic cracking done?
It takes place at a slight pressure, high temperatures and in the presence of a zeolite catakyst, produces large amounts of motor fuels and aromatic hydrocarbons.
What are uses of alkanes?
Fuels
What are positives and negatives of small chain alkanes?
Alkanes such as methane are very easy to combust completely and therefore release more energy with less toxic by products, however they are harder to store than hexane due to their gaseous and high pressure state
What are negatives of combustion engines and how can these be counteracted?
Combustion engines get incredibly hot and therefore form nitrous oxides which are toxic, as well as sulfurous oxides which can cause acid rain. Furthermore incomplete combustion leads to carbon particulates, carbon monoxide and potentially unreacted hydrocarbons. However, catalytic converters remove the toxicity of these chemicals
How are halogenoalkanes formed?
Halogenoalkanes are formed when halogens are intitated, for example chlorine when hit by U.V radiation forming chlorine free radicals. These radicals will then substitute hydrogens in the alkane, forming a halogenoalkane.
