2.5 Hydrocarbons

Question 1

what is a fossil fuel

Answer 1

a fuel which has derived from organisms that lived long ago

Question 2

state 2 advantages of fossil fuels

Answer 2

• available in a variety of forms
• available at all times (solar+wind have limited availability)

Question 3

4 disadvantages of fossil fuels

Answer 3

• non renewable + finite resource
• release greenhouse gases
• cause acid rain
• carbon monoxide is formed

Question 4

what is complete combustion

Answer 4

combustion which occurs with excess oxygen

Question 5

what is incomplete combustion

Answer 5

combustion which occurs with insufficient oxygen

Question 6

what are the 2 reactions of alkanes

Answer 6

1: combustion
2: halogenation

Question 7

what are the products of complete combustion

Answer 7

carbon dioxide + water

Question 8

what are the products of incomplete combustion

Answer 8

carbon monoxide + water

Question 9

how is carbon monoxide toxic

Answer 9

it attaches to haemoglobin and prevents it from carrying oxygen round the body

Question 10

what are the 3 stages of halogenation

Answer 10

1. initiation
2. propagation
3. termination

Question 11

what is halogenation

Answer 11

the reaction between an organic compound and any halogen

Question 12

explain stage 1 (initiation) of halogenation

Answer 12

• UV light breaks the bond between halogens homolytically.
• homolytic bond fission occurs when each of bonded atoms receive one of the bond electrons, forming radicals

Question 13

what are radicals

Answer 13

species with an unpaired electron

Question 14

what is homolytic bond fission

Answer 14

when a bond is broken and each of the bonded atoms receives one of the bonded electrons

Question 15

explain stage 2 (propagation) of halogenation

Answer 15

radicals are very reactive, taking part in propagation reactions
a chain reaction occurs

Question 16

explain stage 3 (termination) of halogenation

Answer 16

the reaction stops due to 2 radicals meeting.

Question 17

write an equation for the reaction of ethane with bromine

Answer 17

C₂H₆ + Br₂ –> C₂H₅Br + HBr

Question 18

how are alkenes formed

Answer 18

when petroleum is cracked

Question 19

what is heterolytic bond fission

Answer 19

when a bond is broken and one of the bonded atoms receives both of the bonded electrons

Question 20

what is the use of electrophilic addition and bromine

Answer 20

a test for alkenes.
bromine is brown. alkene presence shows a discolouration.

Question 21

what is the use of electrophilic addition and hydrogen

Answer 21

hydrogenation.
(catalysed by platinum/palladium/nickel)

hardened liquid vegetable oil = solid fats

Question 22

what is polymerisation

Answer 22

joining of large numbers of monomers = giant polymer molecule

Question 23

name 3 important polymers

Answer 23

• poly(propene)
• poly(chloroethene)
• poly(phenylethene)

Question 24

what is the purpose of polypropene

Answer 24

used in kitchen equipment + food containers (rigid)

Question 25

what is the purpose of polychloroethene

Answer 25

water pipes, insulating electric cable covering + waterproof clothing

Question 26

what is the purpose of polyphenylethene

Answer 26

packing materials