Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture...

47
Section 3.1.6 Alkanes •know that alkanes are saturated hydrocarbons •know that petroleum is a mixture consisting mainly of alkane hydrocarbons •understand that different components (fractions) of this mixture can be drawn off at different levels in a fractionating column because of the temperature gradient •understand that cracking involves the breaking of C–C bonds in alkanes •know that thermal cracking takes place at high pressure and high temperature and produces a high percentage of alkenes (mechanism not required) •know that catalytic cracking takes place at a slight pressure, high temperature and in the presence of a zeolite catalyst and is used mainly to produce motor fuels and aromatic hydrocarbons (mechanism not required) •understand the economic reasons for the cracking of alkanes (e.g. ethene used for poly(ethene); conversion of heavy fractions into higher value products) •know that alkanes are used as fuels and understand that their combustion can be complete or incomplete and that the internal combustion engine produces a number of pollutants (e.g. NOx, CO and unburned hydrocarbons) •know that these pollutants can be removed using catalytic converters

Transcript of Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture...

Page 1: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

Section 3.1.6 Alkanes •know that alkanes are saturated hydrocarbons •know that petroleum is a mixture consisting mainly of alkane hydrocarbons •understand that different components (fractions) of this mixture can be drawn off at different levels in a fractionating column because of the temperature gradient •understand that cracking involves the breaking of C–C bonds in alkanes •know that thermal cracking takes place at high pressure and high temperature and produces a high percentage of alkenes (mechanism not required) •know that catalytic cracking takes place at a slight pressure, high temperature and in the presence of a zeolite catalyst and is used mainly to produce motor fuels and aromatic hydrocarbons (mechanism not required) •understand the economic reasons for the cracking of alkanes (e.g. ethene used for poly(ethene); conversion of heavy fractions into higher value products) •know that alkanes are used as fuels and understand that their combustion can be complete or incomplete and that the internal combustion engine produces a number of pollutants (e.g. NOx, CO and unburned hydrocarbons) •know that these pollutants can be removed using catalytic converters •know that combustion of hydrocarbons containing sulfur leads to sulfur dioxide that causes air pollution and understand how sulfur dioxide can be removed from flue gases using calcium oxide •know that the combustion of fossil fuels (including alkanes) results in the release of carbon dioxide into the atmosphere •know that carbon dioxide, methane and water vapour are referred to as greenhouse gases and that these gases may contribute to global warming

Page 2: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

Alkanes with four or more carbon atoms display structural isomerism because the carbon chain may be either straight or branched.

2-methylbutane:branched chain

pentane:straight chain

The naming of alkanes depends on whether they are straight or branched.

Alkanes and isomersimAlkanes and isomersim

Page 3: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

Trends in boiling pointsTrends in boiling points

Page 4: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

The boiling point of straight-chain alkanes increases with chain length due to increasing van der Waals forces between molecules.

As the length of the chain increases, so does its surface area, and so the van der Waals forces are stronger.Branched-chain alkanes have lower boiling points because the chains cannot pack as closely together. There are fewer points of contact between molecules so the van der Waals forces are weaker.

Trends in boiling pointsTrends in boiling points

Page 5: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

Crude oil is a mixture composed mainly of straight and branched chain alkanes.

The exact composition of crude oil depends on the conditions under which it formed, so crude oil extracted at different locations has different compositions.

It also includes lesser amounts of cycloalkanes and arenes, both of which are hydrocarbons containing a ring of carbon atoms, as well as impurities such as sulphur compounds.

Crude oil and alkanesCrude oil and alkanes

Page 6: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

Fractional distillationFractional distillation

The process in which the components of a mixture are separated into groups or fractions of different boiling points ranges.

What is distillation?

What is fractional distillation?

Distillation is a method of separating mixtures – usually liquids - based on differences in the boiling points of the components of the mixture.

Page 7: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

Fractional distillationFractional distillation

a fractionating column

Page 8: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

Fractional distillationFractional distillation

Page 9: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

Uses of the fractionsUses of the fractions

Page 10: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

Uses of the fractionsUses of the fractions

Page 11: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

Uses of the fractionsUses of the fractions

Page 12: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

Uses of the fractionsUses of the fractions

Page 13: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

Fractions and their usesFractions and their uses

Page 14: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

GCSE Additional Science - Chemistry

C2.5.2

Basics of Organic Chemistry

C2.5.2

Page 15: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

By the end of these two pages you should be able to:

C2.5.2 Targets

• describe the process of cracking

• recall that when alkanes are cracked, mixtures of alkanes and alkenes are formed

• explain the differences between alkanes and alkenes

• describe how bromine water is used to show if something is an alkane or an alkene

• explain how ethene can be reacted with water to make ethanol. H

Page 16: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

Cracking of Hydrocarbons

Hydrocarbons, e.g. alkanes and alkenes, are extracted from....

CRUDE OIL

Crude oil is separated into its parts by

FRACTIONAL DISTILLATION

Page 17: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

Cracking of Hydrocarbons

TOO MUCHTOO MUCH!

TOO LITTLETOO LITTLE!small molecules

large molecules

Page 18: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

Cracking of Hydrocarbons

HEAVY FUEL

HEAVY FUEL

PETROL

PETROL

Heavy oil

Petrol

Produced Needed

AMOUNT

Page 19: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

Cracking of Hydrocarbons

Large molecules

Smaller molecules

C10H22C8H18

C2H4

OctaneDecaneEthene

aluminium oxide

500ºC

Catalystbed

Page 20: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

Cracking of Hydrocarbonsdecane

H

C

H

H C

H

H

C C

C10H22

C C

HH H

HH

H C

C

H

HH C

H

H

C C C C

HH H

HH CH

C

HC C

HH H

HH

H C

C

H

HH C

H

H

C C C C

HH H

HH CH

C

C

H

H

H

H

C C

octane C8H18 ethene C2H4

H

C

H

H C

H

H

C CC C

HH H

HH

H C

C

H

HH C

H

H

C C C C

HH H

HH H

C

SATURATED– contains only single bonds

UNSATURATED– contains a double bond

Page 21: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

C10H22(g)    C8H18(g)   +  C2H4(g)

*The (g) is called a ‘state symbol’ and stands for ‘gas’

Cracking of Hydrocarbons

Cracking reaction – summary:

saturated saturated unsaturated

Page 22: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

Fractions and their usesFractions and their uses

Page 23: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

Demand for lower boiling point (short chain) fractions is greater than the proportion in crude oil.Crude oil contains more higher b.p. (longer chain) fractions, which are in lower demand and less economically valuable...So, there’s a shortage of shorter chain fractions and a surplus of longer chain ones.

Supply and demandSupply and demand

Page 24: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

Cracking is a process that splits long chain alkanes into shorter chain alkanes, alkenes and hydrogen.

Cracking has the following uses:

C10H22 → C7H16 + C3H6

o it increases the amount of gasoline and other economically important fractionso it increases branching in chains, an important factor for petrolo it produces alkenes, an important feedstock

for chemicals.There are two main types of cracking: thermal and catalytic.

What is cracking?What is cracking?

Page 25: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

CrackingCracking

Page 26: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

CrackingCracking

Page 27: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

CrackingCracking

Page 28: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

CrackingCracking

Page 29: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

CrackingCracking

Page 30: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

CrackingCracking

Page 31: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

CatalyticCatalytic cracking has several advantages over thermalthermal cracking:

However, unlike thermal cracking, catalytic cracking cannot be used on all fractions, such as bitumen, the supply of which outstrips its demand.

it produces a higher proportion of branched alkanes, which burn more easily than straight-chain alkanes and are therefore an important component of petrol the use of a lower temperature and pressure mean it is cheaper

it produces a higher proportion of arenesarenes, which are valuable feedstock chemicals.

Thermal v Catalytic crackingThermal v Catalytic cracking

Page 32: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

Alkenes such as ethene are always produced in cracking. They are an important feedstock for use in the chemical industry, particularly in the production of polymers.Arenes such as

benzene are also produced during catalytic cracking. Benzene is added in small quantities to petrol as a replacement for the lead compounds. It too is now the subject of health concerns, and its use is being reduced.

Other products from crackingOther products from cracking

Page 33: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

Complete combustionIn excess oxygen, short chain alkanes can undergo complete combustioncomplete combustion:

The combustion of alkanes is a highly exothermic process. This makes them good fuels because they release a relatively large amount of large amount of energy energy per gram of fuel.

alkane + oxygen → carbon dioxide + water

For example:

propane + oxygen → carbon dioxide + water

C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(g)

Complete combustionComplete combustion

Page 34: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

If oxygen is limited then incomplete incomplete combustioncombustion will occur:

alkane + oxygen → carbon monoxide + wateralkane + oxygen → carbon + water

For example:

propane + oxygen → carbon monoxide + water

C3H8(g) + 3½O2(g) → 3CO(g) + 4H2O(g)

propane + oxygen → carbon + water

C3H8(g) + 2O2(g) → 3C(s) + 4H2O(g)

Incomplete combustionIncomplete combustion

Page 35: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

Alkanes with chain lengths of 5–10 carbon atoms are used as fuels in internal combustion engines.This releases carbon dioxide into the atmosphere:nonane + oxygen → carbon dioxide + water

C9H20(g) + 14O2(g) → 9CO2(g) + 10H2O(g)

Although modern internal combustion engines are more efficient than in the past, incomplete combustion still occurs:

nonane + oxygen → carbon monoxide + water

2C9H20(g) + 19O2(g) → 18CO(g) + 20H2O(g)

The internal combustion engine: carbonThe internal combustion engine: carbon

Page 36: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

The temperature in an internal combustion engine can reach over 2000 °C. Here, nitrogen and oxygen, which at normal temperatures don’t react, combine to form nitrogen nitrogen monoxide:monoxide: N2(g) + O2(g) → 2NO(g)

Nitrogen monoxide reacts further forming nitrogen dioxidenitrogen dioxide:

2NO(g) + O2(g) → 2NO2(g)

Nitrogen dioxide gas reacts with rain water and more oxygen to form nitric acidnitric acid, which contributes to acid rain:4NO2(g) + 2H2O(l) + O2(g) → 4HNO3(aq)

The internal combustion engine: nitrogenThe internal combustion engine: nitrogen

Page 37: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

The catalytic converterThe catalytic converter

Page 38: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

The catalytic converterThe catalytic converter

Page 39: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

The catalytic converterThe catalytic converter

Page 40: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

The catalytic converterThe catalytic converter

CO, NOx, HC

CO2, N2, H2O

Page 41: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

The catalytic converterThe catalytic converter

Page 42: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

Sulphur is found as an impurity in crude oil and other fossil fuels. It burns in oxygen to form sulphur dioxide:S(s) + O2(g) → SO2(g)

Sulphur dioxide may be oxidized to sulphur trioxide: 2SO2(g) + O2(g) → 2SO3(g)

Both of these oxides dissolve in water forming acidic solutions:

SO2(g) + H2O(l) → H2SO3(aq)

SO3(g) + H2O(l) → H2SO4(aq)

Sulphur contamination of fossil fuelsSulphur contamination of fossil fuels

Page 43: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

Acid rain is caused by acidic non-metal oxides such as sulfur oxides and nitrogen oxides dissolving in rain water.Rain water is

naturally acidic because carbon dioxide dissolves in it, forming weak carbonic acid.

What is acid rain?What is acid rain?

Sulphfur and nitrogen oxides form more acidic solutions, which can damage trees and affect aquatic life in lakes and rivers.

Page 44: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

Sulphur dioxide emissions from vehicle fuels such as petrol and diesel are reduced by removing nearly all of the sulphur impurities from the fuel before it is burnt.Removing the sulphur from coal before it is burnt is not practical. Instead, the acidic sulphur oxides are removed from the waste gases using a base such as calcium oxide.

Removing sulfur dioxide pollutionRemoving sulfur dioxide pollution

Page 45: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

Burning fossil fuels releases carbon dioxide into the atmosphere.

It has been suggested that increases in the amount of carbon dioxide and other greenhouse gases may be responsible for apparent changes to the climate.

Fossil fuels are being burned faster than they are being formed, which means that their combustion leads to a net increase in the amount of atmospheric carbon dioxide.

Carbon dioxide in the atmosphereCarbon dioxide in the atmosphere

Page 46: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

Carbon dioxide, water vapour and methane have been described as the main greenhouse gases.

The greenhouse effect is a theory that has been suggested to explain apparent rises in the average temperature of the Earth.

This is because these have been suggested as the gases responsible for the majority of the greenhouse effect.

Increasing the amount of any of the greenhouse gases traps more heat energy from the Sun in the Earth’s atmosphere, raising the average temperature.

Greenhouse gasesGreenhouse gases

Page 47: Section 3.1.6 Alkanes know that alkanes are saturated hydrocarbons know that petroleum is a mixture consisting mainly of alkane hydrocarbons understand.

END