Akanes 6B

Question 1

what is the general formula of alkanes?

Answer 1

Cn H2n +2

Question 2

what are the two types of fission?

Answer 2

homolytic and heterolytic

Question 3

what is homolytic fission?

Answer 3

in homolytic fission, the bond breaks evenly and each binding atom receives one electron from the bonded pair. this means that two electrically uncharged radicals are formed. these are particles that have an unpaired electron (big dot next to the molecular formula)

Question 4

what is heterolytic fission?

Answer 4

in heterolytic fission the bind breaks unevenly with one of the bonded atoms receiving both of the electrons from the bonded pair. two different substances can form - a positively charged cation or a negatively charged anion .

Question 5

what is the reaction called in which halogens and alkanes react?

Answer 5

photochemical reaction. they are started by light - most reactions require ultraviolet light ignorer for them to start

Question 6

what are the stages of a reaction mechanism?

Answer 6

initiation, propagation and termination

Question 7

how are radicals reduced in halogenoalkane reactions

Answer 7

they are produced by initiation reactions.
sunlight produce enough energy to break the Cl-Cl bond - photodissociation
the bond splits equally and each electron gets to keep one electron - homolytic fission the aim becomes a highly reactive radical because of its unpaired electron

Question 8

what happens in a propagation reaction?

Answer 8

radicals are used up and created in a chain reaction
Cl radical attacks a methane molecule
the new methane radical can attack another Cl2 molecule
the new Cl radical can can attack another methane molecule and so on and so on until the Cl2 or the methane are wiped out

Question 9

what happens in a termination reaction?

Answer 9

the radicals are destroyed
if two free radicals join together, they make a stable molecule
there are lots of possible

Question 10

what is the problem with reaction mechanisms?

Answer 10

you end up with a mixture if products

if your trying to make particular products you don’t only get the product that you want but a mixture of products

Question 11

what is petroleum?

Answer 11

a different name for crude oil. mixture of hydrocarbons, it is usually made up of alkanes - they range from small alkanes to massive alkanes

Question 12

how does fractional distillation work?

Answer 12

first the crude oil is vaporised at a out 350 oC
the vaporised crude oil then goes into the fractionating column and rises up through the trays. the largest hydrocarbons don’t vaporise at all as their boiling points are too high.
as the crude oil vapour goes up the fractionating column it gets cooler. as the alkane molecules have different chain lengths they have different boiling points so each fraction condenses at a different temperature

Question 13

what are two types of cracking?

Answer 13

thermal cracking and catalytic cracking

Question 14

what is thermal cracking

Answer 14

it takes place at a high temperature and a high pressure. it produces a lot of alkanes

Question 15

what is catalytic cracking

Answer 15

catalytic cracking uses something called a zeolite catalyst (hydrated aluminosilicate), a slight pressure and high temperature
it mostly produces aromatic hydrocarbons and motor fuels
using a catalyst cuts costs, because the reaction can be done at a low temperature also it speeds up the reaction.

Question 16

what can alkanes be reformed into?

Answer 16

Cycloalkanes and Aromatic Hydrocarbons

Question 17

what is knocking?

Answer 17

it is where atoms explode out of their own accord when the fuel/air is mixed in a compressed engine
straight chain alkanes are the most likely to cause knocking. adding branches to the chain and cyclic hydrocarbons to the petrol mixture makes knocking less likely to happen so combustion is more important

Question 18

why are alkanes useful as fuels?

Answer 18

if you burn alkanes with oxygen you get carbon dioxide and water - combustion reaction - if there is not much oxygen around the alkane will s till burn but it will produce a mixture of mainly carbon monoxide, carbon and water - incomplete combustion.
combustion reactions happen between gases, so liquid alkane have to be vaporised first
combustion reactions are exothermic

Question 19

why do alkanes produce harmful Emissions?

Answer 19

Carbon monoxide is harmful - it is better at binding to the haemoglobin in the bloodstream than oxygen, so it binds before - less oxygen can move around the body leading to oxygen deprivation
sulfer dioxide and oxides of nitrogen lead to acid rain - dissolves in the moisture of the atmosphere and is converted to sulphuric acid
oxides of nitrogen dissolve in the moisture in the atmosphere and are converted to nitric acid

Question 20

what do catalytic converters do?

Answer 20

they remove some pollutants from car emissions

they get rid of them by using a platinum catalyst to change them to harmless gases, like water vapour and nitrogen

Question 21

why are fossil fuels non renewable?

Answer 21

the main fossil fuels - coal, oil and natural gas are relatively easily extracted however there is a finite amount of it

Question 22

what is bioethanol?

Answer 22

the fermentation of sugar from crops to create ethanol.

Question 23

what is biodiesel?

Answer 23

it is made from the refining of renewable fats and oils such as vegetable oil