Topic 6 organic chemistry : Crude oil and fuels (alkanes)

petroleum is a mixture of ..?

alkane hydrocarbons

do branched chains have a high or low boiling point? why?

low

because they have a lower surface area / donot pack closely together so their intermolecular forces are weak

crude oil can be separated into useful bits by ...?

fractional distillation

Explain how fractional distillation works

1) oil is preheated in a furnace

2) crude oil is vaporized at 350 C

3) The vaporized crude oil goes into a fractionating column and rises up through the trays.

4)The largest hydrocarbons don't vaporise at all, because their boiling points are too high (larger london forces) — they just run to the bottom and form a gooey residue.

5) As the crude oil vapour goes up the fractionating column, it gets cooler. Because the alkane molecules have different chain lengths, they have different boiling points, so each fraction condenses at a different temperature.

6)The fractions are drawn off at different levels in the column.

7) The hydrocarbons with the lowest boiling points don't condense. They're drawn off as gases at the top of the column.

why do we want light fractions of crude oil like petrol and naphtha and how do we get them?

- light fractions are in high demand so more valuable

-cracking is breaking long chain alkanes into smaller more useful hydrocarbons (can include alkenes) this helps to convert low demand longer chain hydrocarbons into more highly demanded ones

explain two major reasons for cracking hydrocarbons

-shorter chain alkanes and alkenes are formed

-alkenes are useful starting materials in organic synthesis like plastic

what are the two types of cracking?

thermal cracking and catalytic cracking

what is thermal cracking?

-take places at a high pressure(1000) and high temperature(70)

-produces a lot of alkenes

-these alkenes are used to make valuable products like polymers(plastic) , poly(ethene) from ethene

what is catalytic cracking?

1) zeolite catalyst, at a slight pressure and high temperature

2) It mostly produces aromatic hydrocarbons and motor fuels.

3) Using a catalyst cuts costs, because the reaction can be done at a low pressure and a lower temperature. The catalyst also speeds up the reaction, saving time (and money)

what are aromatic compounds?

Aromatic compounds contain benzene rings. Benzene rings contain a ring of 6 carbon atoms with delocalized ring of electrons

how can alkanes be REFORMED into cycloalkanes and aromatic molecules?

-petrol and deiseal are made of a mixture of straight chain alkanes

-straight chain alkanes create knocking in a car engine , knocking is where straight chain alkanes explode upon compression

-Adding branched chain and cyclic hydrocarbons to the petrol mixture makes knocking less likely to happen, so combustion is more efficient.

-cyclic and branched alkanes can be made using straight chain alkanes and a platinum catalyst in a process called reforming

-eg : hexane can be reformed into cyclohexane and benzene

what is a combustion reaction and write the equation for the combustion reaction of propane

-when alkanes are burned with oxygen to get carbon dioxide and water

-eg:C3H8(g) + 5O2(g) Æ 3CO2(g) + 4H2O(g

what is incomplete combustion and write the formula for the incomplete combustion of ethane

-alkanes will still burn with limited amount of O2 and produce carbon monoxide, carbon and water ( also some CO2)

— C2H6(g) + 2O2(g) Æ C(s) + CO(g) + 3H2O(g)

combustion reactions happens between gases so liquid alkanes have to be...

-vaporised first

-Smaller alkanes turn into gases more easily (they're more volatile), so they'll burn more easily too

are combustion reactions exothermic or endothermic?

exothermic

they RELEASE heat

-Larger alkanes release heaps more energy per mole because they have more bonds to react.

-Because they release so much energy when they burn, alkanes make excellent fuels

how does burning fossil fuels cause pollution?

-generate electricity by burning fossil fuels in power stations

-we burn fossil fuels for transport and heating

-burning these causes pollution

name pollutants formed from burning fossil fuels

-carbon monoxide, unburnt hydrocarbons and carbon particulates from the incomplete combustion of fuels, as well as oxides of sulfur (SOx ) and nitrogen (NOx ).

-causes problems for health and environment

carbon monoxide

-carbon monoxide is better at binding to haemoglobin than oxygen, so it bind to the haemoglobin in your bloodstream before oxygen can

-less oxygen can be carried around your body, leading to oxygen deprivation.

-at very high conc carbon monoxide can be fatal

sulfur dioxide and oxides of nitrogen

-The sulfur burns to produce sulfur dioxide gas which then enters the atmosphere, dissolves in the moisture, and is converted into sulfuric acid.

- Oxides of nitrogen (NOx ) are produced when the high pressure and temperature in a car engine cause the nitrogen and oxygen in the air to react together.

- When oxides of nitrogen (NOx ) escape into the atmosphere, they dissolves in moisture and are converted into nitric acid, which can fall as acid rain.

- Acid rain destroys trees and vegetation, as well as corroding buildings and statues and killing fish in lakes

solid carbon (soot) and the release of unburnt hydrocarbons from incomplete combustion

-unburnt hydrocarbons: contribute towards formation of smog

-soot/particulates: global dimming and respiratory problems

what do catalytic converters do?

-catalytic converters helps to reduce the amount of unburnt hydrocarbons ,oxides of nitrogen and carbon monoxide released

-they use a platinum catalyst to convert them into less harmful/harmless gases

-to water vapor, nitrogen and carbon dioxide

catalytic converters have a ceramic honeycomb coated with a thin layer of catalyst metals platinum/palladium/rhodium to give a....

large sa

write the equation for converting nitrogen monoxide and carbon monoxide to nitrogen and carbon dioxide (BALANCE)

2NO(g) + 2CO(g) Æ N2 (g) + 2CO2 (g)

are fossil fuels renewable or non renewable?

non renewable

-coal, oil, and natural gas are relatively easily extracted and produce a large amount of energy when burnt, there is a finite amount of them

-oil is the most in short supply so extracting is difficult and will increase costs

what are the renewable alternatives to fossil fuels

biofuels

define biofuels

fuels made from living matter over a short period of time

how is bioethanol made?

Fermentation of sugar from crops such as maize

how is biodiesel made?

refining renewable fats and oils such as vegetable oils

how is biogas made?

breakdown of organic matter

advantages of using biofuels

-they are crabon nuetral becasue the carbon dioxide produced is what the plants absorbed

-they are renewable

-biodiesel and biogas is made from waste that would otherwise go to landfill

disadvantages of using biofuels

-petrol car engines would have to be modified to use fuels with high ethanol concentrations.

-land not used to grow food crops could cause food shortages in developing countries due to the demand of developed countries demands for alternative to fossil fuels

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