6.2 - Hydrocarbons/ Alkanes, Alkenes Flashcards Preview

Edexcel A Level Chemistry > 6.2 - Hydrocarbons/ Alkanes, Alkenes > Flashcards

Flashcards in 6.2 - Hydrocarbons/ Alkanes, Alkenes Deck (37)
Loading flashcards...
1

What are Alkanes?

SATURATED hydrocarbons

2

what re Alkenes?

UNSATURATED hydrocarbons

3

Alkanes general formula?

CnH2n+2

4

Alkenes general formula?

CnH2n

5

Octane numbers?

=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'

6

Reforming?

a catalyst is used together with high temperature

7

Cracking?

useful, break down hydrocarbons to make more useful fuels

8

thermal cracking?

temperature and pressure

9

Catalytic cracking?

catalyst, temperature, pressure

10

Burning alkanes?

Fractional distillation

11

Fractional distillation?

Inject crude oil
vapourised
rises
cools
condenses
collected as fractions

12

What is the point in burning alkanes?

To make useful substances such as petrol and diesel

13

Free radical substitution steps?

Initiation
Propagation
Termination

14

What are the conditions needed for homolytic fission?

U.V light
300 degrees

15

Initiation?

the molecule is split by homolytic fission, forming 2 radicals

16

Propagation?

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

17

Termination?

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

18

Problems with free radical substitution?

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

19

Catalytic converters?

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

20

Testing for alkenes?

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

21

Why are alkenes insoluble in water?

They cant form H bonds because there are no oxygens

22

Name the 2 bonds in alkenes?

Sigma and pi

23

When do bonds form?

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

24

When is a sigma bond formed?

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

25

When is a pi bond formed?

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

26

which bond is weaker?

pi bond is MUCH weaker

27

Why do trans isomers have lower boiling points?

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

28

Making alkanes from alkenes?

Hydrogenation
150 degrees
nickel catalyst

29

Heterolytic fission?

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

30

Making alcohols?

Hydration reaction
eg. Ethene+water = Ethanol