6.2 - Hydrocarbons/ Alkanes, Alkenes

Question 1

What are Alkanes?

Answer 1

SATURATED hydrocarbons

Question 2

what re Alkenes?

Answer 2

UNSATURATED hydrocarbons

Question 3

Alkanes general formula?

Answer 3

CnH2n+2

Question 4

Alkenes general formula?

Answer 4

CnH2n

Question 5

Octane numbers?

Answer 5

=A measure of the performance of the fuel
=higher octane means a more efficient fuel
=straight chains are prone to knocking, exploding due to activation energy
=knocking is increased by straight chained hydrocarbons, therefore branched molecules burn better ‘higher octane number’

Question 6

Reforming?

Answer 6

a catalyst is used together with high temperature

Question 7

Cracking?

Answer 7

useful, break down hydrocarbons to make more useful fuels

Question 8

thermal cracking?

Answer 8

temperature and pressure

Question 9

Catalytic cracking?

Answer 9

catalyst, temperature, pressure

Question 10

Burning alkanes?

Answer 10

Fractional distillation

Question 11

Fractional distillation?

Answer 11

Inject crude oil
vapourised
rises
cools
condenses
collected as fractions

Question 12

What is the point in burning alkanes?

Answer 12

To make useful substances such as petrol and diesel

Question 13

Free radical substitution steps?

Answer 13

Initiation
Propagation
Termination

Question 14

What are the conditions needed for homolytic fission?

Answer 14

U.V light

300 degrees

Question 15

Initiation?

Answer 15

the molecule is split by homolytic fission, forming 2 radicals

Question 16

Propagation?

Answer 16

during the halogenation of alkanes, the radical will then go onto react with eg. methane
Rapid process

Question 17

Termination?

Answer 17

the end of radical substitution where 2 radicals combine to form a molecule

Question 18

Problems with free radical substitution?

Answer 18

other radicals can be formed

if there’s too much mixture, other products will be formed and therefore have to be separated

Question 19

Catalytic converters?

Answer 19

Redox reaction
one reduction catalyst and one oxidation
Molecules bond with the catalyst and elements separate off as a harmless gas

Question 20

Testing for alkenes?

Answer 20

place sample in test tube with drops of bromine water, the more drops needed to go colourless, the more unsaturated

Question 21

Why are alkenes insoluble in water?

Answer 21

They cant form H bonds because there are no oxygens

Question 22

Name the 2 bonds in alkenes?

Answer 22

Sigma and pi

Question 23

When do bonds form?

Answer 23

bonds form between atoms when atomic orbitals overlap and form molecular orbitals

Question 24

When is a sigma bond formed?

Answer 24

when 2 s orbitals overlap (in a straight line) which is a single covalent bond

Question 25

When is a pi bond formed?

Answer 25

when 2 p orbitals overlap sideways, it forms an area above and below the molecular axis.

Question 26

which bond is weaker?

Answer 26

pi bond is MUCH weaker

Question 27

Why do trans isomers have lower boiling points?

Answer 27

Because the U shape of the cis isomer doesnt pack as well as the straighter shape. Intermolecular forces arent as strong as they should be

Question 28

Making alkanes from alkenes?

Answer 28

Hydrogenation
150 degrees
nickel catalyst

Question 29

Heterolytic fission?

Answer 29

is the breaking of a covalent bond so that both bonding electrons are taken by one atom

Question 30

Making alcohols?

Answer 30

Hydration reaction

eg. Ethene+water = Ethanol

Question 31

Stability of carbocations?

Answer 31

stable- least stable Quarternary, tertiary, secondary, primary! the more methyl groups, the more stable it is!!

Question 32

Making diols?

Answer 32

Addition and oxidation takes place in this reaction

The requirements are dilute acidified potassium manganate

Question 33

monomers and polymers?

Answer 33

know how to draw them

Question 34

Propagation?

Answer 34

reactions continue until all hydrogen atoms have been replaced with halogen atoms

Question 35

Everything about natural gas?

Answer 35

naturally occuring
hydrogen based]
used for heating, cooking and electrics
produced as a result of decaying material

Question 36

Everything about bio diesel?

Answer 36

most economical
renewable fuel
many uses, generators

Question 37

Nuclear power?

Answer 37

no CO2
hard to dispose of waste
need enriched uranium 235- awkward