POM: Energy and Raw Materials from Fossil Fuels

Question 1

What is petroleum?

Answer 1

A mixture of crude oil and natural gas, formed over thousands of years from fossilised organisms.

Question 2

What is cracking?

Answer 2

A chemical process by which hydrocarbons with higher molecular masses (low in demand) are converted to hydrocarbons of lower molecular masses (high in demand) eg. ethylene

Question 3

What is steam cracking?

Answer 3

Cracking in the absence of a catalyst.

Ethane (C2H6) obtained from petroleum and natural gas, is fed into furnaces with steam.

Mixture is heated between 700 and 900 degrees.

Question 4

What is catalytic cracking?

Answer 4

Cracking in the presence of a catalyst.

• Zeolites are used as a catalyst, allowing lower temperatures (500) to be used.
• Although it uses less heat than thermal, it cannot decompose large molecules completely into ethylene so it is INSUFFICIENT IN MEETING THE DEMANDS OF INDUSTRY

Question 5

Why is ethylene, according to it’s chemical properties, can be readily transformed into many useful products?

Answer 5

Ethylene is unsaturated. It’s highly reactive double bond (a site of high electron cloud density), allows it to undergo addition reactions and polymerisation readily.

The double bond breaks open easily to form two single bonds.

Question 6

What reaction do alkanes complete in bromine water?

Answer 6

A substitution reaction in which one hydrogen atom is replaced by a halogen atom.

Features:

• Slow rate
• Needs UV light
• Two products

Question 7

What reaction do alkenes complete in bromine water?

Answer 7

Addition reactions. The double bond breaks and is replaced by a single bond when two new atoms are added to the molecule.

Features:

• Fast rate
• One product

Question 8

Through addition reactions, what are the 4 main types and what can it produce?

Answer 8

• Hydration = water is added to form ethanol
• Halogenation = a halogen (eg. Fl, Cl, Br, I) is added
• Hydrogenation- heated with hydrogen with a catalyst
• Hydrohalonation- hydrohalogen such as HCl react with no catalyst

Question 9

How is ethylene a useful monomer from which polymers are made?

Answer 9

Due to it’ highly reactive double bond, ethylene serves as a monomer to undergo addition polymerisation to form polyethylene.

Question 10

Outline the three stages in the production of polyethylene

Answer 10

Initiation, propagation, termination

Question 11

What is an addition polymer?

Answer 11

Forms from the joining of repeating monomer units to produce longer chain molecules called polymers and no other product. There is no loss or gain of atoms as they add so that all atoms present in the monomer are present in the polymer.

Question 12

What happens in the initiation stage?

Answer 12

The initiator molecule (eg peroxide) decomposes to form reactive free radicals.

The free radicals break the double bond of an ethylene monomer for form an ethylene free radical

Question 13

What happens in the propagation stage?

Answer 13

Ethylene free radical reacts with another monomer, and this process continues and therefore chain length grows

Question 14

What happens in the termination stage?

Answer 14

Chain growth is halted by an inhibitor, when two ethylene radicals combine.

Question 15

How is LDPE produced?

Answer 15

Uses high pressure method.

Involves igh temperatures (300OC) and the presence of an initiator (organic peroxide).

The product has significant chain branching.

• Some carbon atoms one hydrogen atom is replaced by an alkyl group
• Alkane chains cannot pack close together in an orderly way

Question 16

How is HDPE produced?

Answer 16

Ziegler-Natta process

It is produced under low pressures, low temperatures (60C) and uses a catalyst.

The molecules produced are unbranched, and linear and thus are able to pack closely together.

The product is more crystalline

Question 17

What are the properties of LDPE and relate it ot it’s uses

Answer 17

The extensive chain branching makes it relatively soft and flexible so it is used in making plastic cling wrap and plastic bags

Question 18

What are the properties of HDPE and relate it ot it’s uses

Answer 18

No chain brainching, meaning polymer chains are linear and closely packed together, held tightly by dispersion forces.

This results in the polymer being rigid and hard, so it is used in making durable items such as rubbish bins, and containers

Question 19

What is vinyl chloride?

Answer 19

It is an etylene molecule with a H atom substituted with a Cl atom.

Systematic name: chloroethane
Polymer: PVC

Question 20

What is styrene?

Answer 20

An ethylene molecule with an H atom replaced by a benzene ring (6C ring with alternating double bonds)

Systematic name: ethynyl benzene or phenylethene
Poylmer: polystyrene

Question 21

Uses of PVC?

Answer 21

PVC is hard, inflexible and brittle, and the large Cl atoms increase the polymer’s stiffness This rigid forms of PVC can be used for drainage and sewage pipes and guttering.

Softer PVC (addition of plasticiser) decrease dispersion forces making it more flexible. –> electrical insulation and flexible tubing

Question 22

Uses of polystyrene?

Answer 22

• Electrically insulative and very hard and rigid due to the presence of large side group benzene rings along the polymer chains. This makes it suitable for car battery cases and tool handles.
• Crystalline due to minimal chain branching, therefore can be used in transparent/clear objects
• Styrofoam can be produced if gas is bubbled through –> insulation and packaging