2.5 - Hydrocarbons

Question 1

What is a fossil fuel?

Answer 1

A source of energy that is derived from organisms that lived a long time ago.

Question 2

What is a non-renewable resource?

Answer 2

Resources that cannot be reformed in a a reasonable time scale.

Question 3

What is a green house gas?

Answer 3

One that causes an increase in the Earths temperature.

Question 4

What are 2 advantages to using fossil fuels?

Answer 4

They are available in a variety of forms so that the type of fuel can be matched with its use
They are available at all times (green sources like solar have limited daily availability)

Question 5

What are the 4 disadvantages of using fossil fuels?

Answer 5

They are non-renewable
Combustion of fuels creates CO2 (a green house gas)
Acid rain forms from sulfur and nitrogen
Carbon monoxide formation which is toxic to haemoglobin as it acts as an inhibitor

Question 6

What is the equation for alkanes?

Answer 6

CnH2n+2

Question 7

Are alkanes saturated or unsaturated?

Answer 7

Saturated

Question 8

What state is a small alkane?

Answer 8

Gas (natural gas like methane)

Question 9

What state is a large alkane?

Answer 9

Liquids (petrol)

Question 10

What state is the largest alkane?

Answer 10

Solids (wax)

Question 11

Why are alkanes generally unreactive?

Answer 11

They are non-polar.

Question 12

What is complete combustion?

Answer 12

If sufficient oxygen is present, carbon dioxide and water are formed.

Question 13

What is incomplete combustion?

Answer 13

If insufficient oxygen is present, carbon monoxide and water are formed.

Question 14

What is halogenation?

Answer 14

The reaction between an organic compound and any halogen.
Basically free radical substitution.

Question 15

What is the trigger for free radical sub/halogenation?

Answer 15

UV light, will not react in darkness

Question 16

What is the first stage in free radical substitution?

Answer 16

Initiation
- starts the reaction
- UV light has enough energy to break the cl-cl bond homolytically
- homolytic bond fission occurs when each of the bonded atoms recieves one of the bond electrons so that radicals are formed
- this means they are highly reactive
Cl2 = Cl+Cl

Question 17

What is the second stage in free radical substitution?

Answer 17

Propagation
- uses radicals as a reactant and then forms a radical as a product
- chain reaction
Cl* + CH4 = CH* + HCl
CH* + cl2 = Ch3Cl + Cl*

Question 18

What is the final stage in free radical substitution?

Answer 18

The propagation steps continue until 2 radicals meet
Cl* + Ch3* = Ch3Cl

Question 19

Are alkenes saturated or unsaturated?

Answer 19

Unsaturated as they contain a double bond

Question 20

What is the formula for an alkene?

Answer 20

CnH2n

Question 21

How can alkenes be formed in industry?

Answer 21

By cracking petroleum, which is important in polymerisation reactions

Question 22

What does the double bond create for an alkene?

Answer 22

An area of electron density, called a Pi orbital
A double bond means high reactivity

Question 23

What is an electrophilic addition reaction?

Answer 23

• as alkenes have a pi bond, they are suseptible to an attack by an electrophile
• the mechanism involves heterolytic bind fission leading to an addition reaction

Question 24

What is an electrophile?

Answer 24

Any species that can accept a lone PAIR of electrons

Question 25

What is heterolytic bond fission?

Answer 25

When a bond is broken and one of the bonded atoms recieves both of the bonded electrons

Question 26

What are the triggers for electrophilic reactions?

Answer 26

A double bonded alkene and an electrophile

Question 27

What happens to electrophiles in electrophilic reactions that are non-polar?

Answer 27

A dipole is induced by the negative charge in the pi bond.

Question 28

What are the 2 common uses of electrophillic addition?

Answer 28

Bromine - alkene testing
Hydrogen - hydrogenation

Question 29

How is bromine linked to electrophillic addition?

Answer 29

• testing for an alkene
• bromine is brown, turns colorless when an alkene is present
• bromine water is used instead of bromine liquid as b.l is very corrosive

Question 30

How is hydrogen linked to elctrophillic addition?

Answer 30

• hydrogenation
• catalysed by transition metals
• the reaction is important in industry because liquid oils contain many double bonds that can be saturated with hydrogen to form solid products like butter

Question 31

Why are secondary and tertiary carbocations more desirable than primary carbocations?

Answer 31

• alkyl groups tend to release electrons so that they become delta positive
• this spreads or delocalises the positive charge and stabilises the ion
• this means 2/3 carbocations are more stable than 1* cations, thus are the more desirable/common product

Question 32

What is polymerisation?

Answer 32

Joining of a very large number of monomer molecules to make a large polymer molecule

Question 33

What is addition polymerisation?

Answer 33

• occurs in alkenes
• the double bond is used to join molecules
  -example when ethene is polymerised, poly(ethene) is formed
  Drawn n c=c ——— (c-c)n

Question 34

What is poly(propene)?

Answer 34

Monomer propene
Polymer poly(propene)
polypropene is rigid and used in food containers and general kitchen equipment

Question 35

What is poly(chloroethene)?

Answer 35

Monomer chloroethene
Polymer polychloroethene
Old name vinyl chloride, or polyvinyl chloride (PVC)
Used in water pipes, waterproof clothing, insulating cover for electrical cables

Question 36

What is poly(phenylethene)?

Answer 36

monomer phenylethene
polymer poly(phenylethene)
Old name styrene, poly styrene
Hard, used in household items for strength and integrity