2. alkanes

Question 1

crude oil [4]

Answer 1

non renewable resource

formed when animal remains are buried under high temperature and pressure in the absence of O2 over millions of years

it is a valuable resource used in the process of making fuels, plastics, medicines

alkanes are the main constituent of crude oil

Question 2

alkanes are saturated hydrocarbons. what does this mean?

Answer 2

saturated - each C forms max bonds. there are only C-C

hydrocarbons - consist only of H and C

Question 3

process of fractional distillation []

Answer 3

1. Oil is heated to evaporation in blast furnace. it enters fractionating column
2. has a temp gradient where it is hottest at the bottom
3. short chain molecules have lower BP bc weaker imf and condense nearer the top
4. separate into fractions [fractions are mixtures of hydrocarbons with sim chain lengths and uses] of similar boiling points and chain lengths

Question 4

what is fractional distillation based on

Answer 4

a physical process based on different bps and molecule sizes. it splits the weak vdw forced between molecules

Question 5

def of cracking

2 types

Answer 5

breakdown/ conversion of long chain HCs into SC HCs by breaking C-C bonds

this is done bc shorter chain alkanes are more in demand and more useful

there is catalytic and thermal cracking

Question 6

conditions and products of catalytic cracking

Answer 6

zeolite catalyst
high temp of ~450C
moderate pressure

produces branched alkanes, cyclic alkanes, aromatic hydrocarbons

Question 7

conditions + products of thermal cracking

Answer 7

high temperature 800
high pressure 7000kPa

produces alkenes

Question 8

fuel

why are alkanes good fuels

Answer 8

smth that releases heat energy when burned/ combusted

they burn readily in oxygen, highly exothermic

Question 9

why is incomplete combustion not good

what can it form []

Answer 9

releases less energy/mole and forms pollutants

NOx gases
SO2
C
CO
unburnt HCs

Question 10

what makes something a GHG

Answer 10

polar bonds

absorbs ir radiation

Question 11

what do catalytic converters do and what catalysts do they use

Answer 11

they are in cars to remove CO and NOx and unburnt HCs to give CO2, N2 and H2O.

2CO+ 2NO - 2CO2 + N2

unburnt HC chains react with NO to form CO2, N2 and water

it will have a platinum, palladium or rhodium catalyst

Question 12

flue gas desulfurization

Answer 12

SO2 can be removed from flue gases using calcium oxide or calcium carbonate

CaCO3 + SO2 -> CaSO3 + CO

Question 13

why are alkanes unreactive

why do they react with halogens in UV light and what do they form

Answer 13

little polarity

UV light has more energy providing Ea for bonds to break. in presence of UV X-X bond in halogen molecules break to form halogen free radicals

f radicals are atoms/molecules with an unpaired electron

Question 14

general process of alkane + free radical

Answer 14

alkane + free radical -> alkane radical + hydrogen halide

alkane radical + halogen molecule -> h.alkane + halogen radical

Question 15

steps to free radical substitution

Answer 15

INITIATION
UV forms f radicals from halogen molecules

PROPAGATION
molecule + radical -> molecule + radical

TERMINATION
- desired product
- halogen molecule
- side reaction where two alkane radicals form. in Qs always do structural formula

Question 16

how has frs depleted the ozone layer

Answer 16

the synthesis of chlorofluorocarbons to be used as coolants or refrigerants was bad because they are unreactive so rise to stratosphere where UV is stronger. the CCl bond breaks and forms Cl• which reacts with O3 as a catalyst. one Cl• cand destroy thousands O3s.