alkanes

a homologous series of saturated hydrocarbons

CnH2n+2

they are not polar and cannot overcome / disrupt the hydrogen bonding between water molecules.

As the alkane gets longer, the boiling point increases. This is because a longer alkane chain has increased intermolecular forces which require more energy to overcome and cause the state change from liquid to gas.

stronger van der waals forces bwt the molecules which require greater amounts of energy to overcome- as there are more electrons

weaker VDW

fractional distillation

Crude oil is a fossil fuel, formed from the decay of sea creatures over millions of years under high pressure and lack of oxygen

Fractional distillation is carried out in a fractionating column which is very hot at the bottom and cool at the top Crude oil enters the fractionating column and is heated so vapours rise Vapours of hydrocarbons with very high boiling points will immediately condense into liquid at the higher temperatures lower down and are tapped off at the bottom of the column Vapours of hydrocarbons with low boiling points will rise up the column and condense at the top to be tapped off The different fractions condense at different heights according to their boiling points and are tapped off as liquids The fractions containing smaller hydrocarbons are collected at the top of the fractionating column as gases The fractions containing bigger hydrocarbons are collected at the lower sections of the fractionating column The crude oil contains small amounts of other compounds Some of these compounds may contain sulfur, and when burned sulfur dioxide can be produced This is one of the causes of acid rain

they are not useful as heavy alkanes so they are cracked into shorter alkanes and alkenes which are higher in demand

the thermal decomposition of alkanes

temp = 900 pressure = 70atm catalyst= none products= alkanes

temp=450 pressure = 1-2 atm cataylst= zeolites products= alkenes + motor fuels

Alkanes are combusted (burnt) on a large scale for their use as fuels

When alkanes are burnt in excess (plenty of) oxygen, complete combustion will take place and all carbon and hydrogen will be oxidised to carbon dioxide and water respectively

CO2 and H2O

When alkanes are burnt in only a limited supply of oxygen, incomplete combustion will take place and not all the carbon is fully oxidised Some carbon is only partially oxidised to form carbon monoxide For example, the incomplete combustion of octane to form carbon monoxide

H2O CO and/or C

Incomplete combustion often takes place inside a car engine due to a limited amount of oxygen present

CO is a toxic and odourless gas which can cause dizziness, loss of consciousness and eventually death The CO binds well to haemoglobin which therefore cannot bind oxygen and carbon dioxide Oxygen is transported to organs Carbon dioxide is removed as waste material from organs

Normally, nitrogen is too unreactive to react with oxygen in air However, in a car engine, high temperatures and pressures are reached causing the oxidation of nitrogen to take place: N2(g) + O2(g) → 2NO(g) N2(g) + 2O2(g) → 2NO2(g) The oxides of nitrogen are then released in the exhaust fumes into the atmosphere Car exhaust fumes also contain unburnt hydrocarbons from fuels and their oxides (VOCs) Nitrogen oxides and sulfur dioxides can also dissolve and react in water with oxygen to form nitric acid which is a cause of acid rain Acid rain can cause corrosion of buildings, endangers plant and aquatic life (as lakes and rivers become too acidic) as well as directly damaging human health

balckens buildings can cause respiratory problems global dimming

greenhouse gas

the sulphur in impurties in petroleum can react with oxygen in atmosphere or air producing SO2