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Chemistry Y12 > akenes in industry > Flashcards

akenes in industry Flashcards

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1
Q

what is direct hydration?

A

a large scale industrial process to make an alcohol from ethene

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2
Q

alkenes undergo direct hydration with…?
to produce…?

A

steam (water) in the presence of an phosphoric acid catalyst to form an alcohol

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3
Q

the direct hydration of alkenes is also know as an…?

A

addition reaction

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4
Q

state the reaction conditions for the direct hydration of alkenes?

A
  • steam
  • 6500 kPa (65atm)
  • phosphoric acid catalyst H3PO4
  • (300°c)
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5
Q

the direct hydration of alkenes is a continuous industrial process. explain what this means?

A

A continuous process is one in which more reactants are added as the products are removed.

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6
Q

what are the advantages of making ethanol by the direct hydration of ethene?

A
  • The reaction is fast.
  • It produces a high yield of ethanol.
  • The ethanol is pure.
  • The continuous process is cheap on manpower.
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7
Q

what are the Disadvantages of making ethanol by the direct hydration of ethene?

A
  • The reaction uses ethene (from crude oil) – a finite resource.
  • The continuous process requires expensive equipment
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8
Q

draw the full exam mechanism for the formation of an alcohol by the reaction of an alkene (ethene) with steam in the presence of an acid catalyst.

A
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9
Q

can other alcohols be made using this process?

A

yes

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10
Q

why is the pressure in these reactions vey controlled?

A

as very high pressures could result in a polymerisation reaction.

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11
Q

Changing the temperature and pressure can effect the position of equilibrium. Why is a constant pressure of 6500 kpa used in the direct hydration of alkanes?

A

Increasing the pressure shifts equilibrium to the side with the least gaseous molecules to decrease the pressure so the above equilibrium shifts to the right to increase the yield of ethanol

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12
Q

addition polymerisation

A

Add in card

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13
Q

what are polymers?

A

Polymers are long chain molecules formed when a large number of small molecules (monomers) join together.

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14
Q

what are the two types of polymers?

A

natural (e.g DNA) and synthetic (man-made)

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15
Q

what are the uses of natural polymers?

A

fabrics and jewellery.

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16
Q

uses of synthetic polymers ?

A

Artificial polymers such as artificial silk and hard rubber were synthesised by researchers in the 19th century nylon and Kevlar in 20th century

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17
Q

what is a polymerisation reaction?

A

A polymerisation reaction involves joining together a large number of small
molecules (monomers), to form a very large molecule (polymer

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18
Q

alkenes undergo addition polymerisation to form? but only…?

A
  • saturated addition polymers only.
  • in the presence of a catalyst
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19
Q

why are addition polymers called chain-growth polymers?

A

because they are made by the addition of monomers to the reactive end of a growing chain.

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20
Q

how are addition polymers usually formed?

A

via free radical substitution mechanism

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21
Q

what are the reaction conditions for addition polymerisation?

A

high pressure and a free radical initiator
e.g. an organic peroxide ROOR (needed to start the reaction).

22
Q

what is the reactive end of a growing chain?

A

a radical that is reformed at the end of
a chain after each addition of a monomer molecule.

23
Q

how is polyethene made?

A

when ethene molecules link together

24
Q

why are addition polymers chemically unreactive?

A

The carbon-carbon bonds are non-polar

25
Q

in addition polymers the carbon-carbon bonds cannot be hydrolysed. explain why this is useful?

A

This is a useful property for the resultant polymer since it cannot be attacked by acids, alkalis and oxidising agents.

26
Q

draw the repeating unit for poly(ethene)

A
27
Q

what are substituted alkenes?

A

Many polymers can be formed from monomers in which some or all of the hydrogen atoms in ethene have been
replaced

28
Q

what are the different R groups monomers can be represented by?

A

R = H CH3, C6H5, Cl, CN, or OCOCH3

29
Q

Each polymer has its own…?, so different polymers can be used to make a ….?

A

physical properties
a range of commercial products

30
Q

draw The polymerisation of propene to make poly(propene)

A
31
Q

explain why addition polymers made from alkenes are unreactive?

A

Addition polymers formed from alkenes are saturated compounds. The bonds within the polymer are usually non-polar. Therefore
addition polymers are unreactive.

32
Q

explain bonding between polyalkene molecules?

A

Polyalkene molecules are usually non-polar so there are only weak van der Waals forces between neighbouring molecules. Larger polyalkene molecules will have more van der Waals forces between molecules.

33
Q

Do Longer chains with no branches have stronger or weaker intermolecular forces?

A

Longer chains with no branches have stronger intermolecular forces because the molecules can pack closely together. This makes the material stronger and more rigid.

34
Q

do Polyalkenes with more branching have weaker or stronger van der Waals forces?

A

Polyalkenes with more branching will have weaker van der Waals forces between neighbouring molecules because the chains
cannot pack as closely. This makes the material more flexible.

35
Q

when can the polymer be polar?

A

The polymer chain can be polar if the monomer contains electronegative atoms (e.g. poly(chloroethene))

36
Q

what are the typical uses of poly(ethene)?

A

used to make plastic bags and cling film.

37
Q

why do these items usually end up in landfills?

A

In packaging applications where poly(ethene) is commonly used the material cannot easily be collected, cleaned and recycled, and so ends up in landfill.

38
Q

what are the typical uses for poly(propene)?

A
  • It is used to make rigid plastic containers (crates), chairs, pipes and car bumpers.
  • made into fibres that are used as the backing for carpets and in thermal clothing.
  • Poly(propene) is also used to make crisp packets.
39
Q

why is poly(propene) less likely to be in landfills?

A

Poly(propene) is more readily recycled. Containers → collected → cleaned
→ cut up into small pieces → melted → remoulded or extruded and spun
into fibres.

40
Q

how is poly(chloroethene)/ polyvinylchloride (PVC) made?

A
  • Poly(chloroethene), also known as PVC (polyvinylchloride) is an addition polymer formed from chloroethene monomers.
41
Q

explain why PVC is a hard, brittle material?

A

The polar carbon-chlorine bonds mean that there are permanent dipole-dipole forces between the polymer chains. This makes PVC a hard but brittle material

42
Q

so PVC can be used to make…?

A

drain pipes and window frames

43
Q

what can be added to polymers to change their properties?

A

Plasticiser molecules can be added to polymers to modify their properties. Adding a plasticiser makes a polymer more bendy

44
Q

explain how plasticiser molecules make the polymer more flexible

A

The plasticiser molecules get between the polymer chains and push them apart. This reduces the strength of the intermolecular forces between the chains – so the chains can slide around more. This makes the polymer more flexible.

45
Q

what is Plasticised PVC used to make?

A

It is used to make electrical cable insulation, flooring tiles and clothing.

46
Q

why are poly(alkenes) non-biodegradable?

A

The poly(alkenes) are chemically unreactive (inert) because the carbon carbon bonds in the molecules are non-polar and strong.
* The poly(alkenes) are chemically inert and therefore non-biodegradable.

47
Q

why is this a problem?

A

If they are placed in rubbish dumps or landfill sites they will not decay over the years.

48
Q

what is another problem?

A

Poly(alkenes) are chemically unreactive but are still highly flammable.

49
Q

explain the downside of incineration?

A

ncineration produces greenhouse gases and other toxic gases (e.g. hydrogen cyanide !!).

50
Q

explain the problem with recycling?

A

Recycling of polymers is expensive but does offer an alternative solution instead of landfill and incineration.
A problem with recycling is that the various types of plastics have to be separated from each other prior to recycling.

51
Q

FINISH

A

Chemistry Y12 (11 decks)

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