Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

chemistry!👩🏽‍🔬🧪 > alkanes (organic chem) > Flashcards

alkanes (organic chem) Flashcards

hydrocarbons, fractional distillation of crude oil, uses of alkanes,cracking, combustion

You may prefer our related Brainscape-certified flashcards:
Periodic Table flashcards Chemistry 101 flashcards AP® Chemistry flashcards Organic Chemistry 101 flashcards
1
Q

define ‘alkanes’

A

saturated hydrocarbons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

define ‘petroleum fraction’

A

mixture of hydrocarbons with similar chain length & b.p range

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

gen. formula of alkanes

A

CnH(2n+2)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

reactivity of alkanes

(and why?)

A

unreactive apart from combustion –> strong, non-polar C-C & C-H bonds

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

process of fractional distillation of crude oil

A

> the petroleum fractions condense at diff. heights
the temp. of the column decreases upwards
smaller molecules condense at top –> lower temp = lower b.p –> smaller size –> smaller VDWs
larger molecules condense at bottom –> higher temp = higher b.p –> larger size –> larger VDws

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

smaller molecule characteristics

A
  • lighter colour
  • very flammable
  • low viscosity
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

larger molecule characteristics

A
  • darker colour
  • less flammable
  • high viscosity
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

vacuum distillation

A
  • heavy residue from fractionating column distilled under vac.
  • lowering the pressure over a liquid = lower b.p
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

why might vacuum distillation be used?

A
  • allows heavier fractions to be further seperated
  • no need for high temps –> could break them down
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

define ‘cracking’

A

conversion of long hydrocarbons to smaller, more useful hydrocarbon molecules by breakage of C-C bonds

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

high Mr alkanes –>

A

smaller Mr alkanes + alkenes + (hydrogen)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

name a solid material made from alkanes

A

polymer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

why does cracking req. high temps?

A

involves splitting of strong cov. bonds (C-C)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

list the economic reasons for cracking

A
  1. petroleum fractions with shorter C chains (eg. petrol) are higher in demand
  2. products of cracking = more valuable than starting materials
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

conditions for thermal cracking

A
  • high pressure (7000kPa)
  • high temp. (400-900 degrees)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

products of thermal cracking

A
  • mostly alkenes
  • sometimes prod. hydrogen
17
Q

process of thermal cracking

A
  • proceeds via free radical mechanism
  • 1st step is homolytic fission of C-C bond
18
Q

conditions for catalytic cracking

A
  • slight pressure
  • high temp (450 degrees)
  • zeolite catalyst
19
Q

products of catalytic cracking

A
  • branched and cyclic alkanes
  • aromatic hydrocarbons
20
Q

why is catalytic cracking used?

A
  • branched/cyclic hydrocarbons burn more smoothly than unbranched ones –> used to give fuels higher octane no.
  • cheaper than t. cracking –> uses less energy –> lower temp n pressure
21
Q

why are alkanes used as fuels?

A
  • they burn readily in presence of oxygen
  • this combustion of alkanes = highly exo.
  • can be used as fuels (fuels release heat energy when burnt)
22
Q

complete combustion

A
  • fuel + O2 –> CO2 + H2O
  • excess O2
23
Q

incomplete combustion

A
  • fuel + O2 –> C or CO + steam
    –> CO = colourless, odourless, toxic gas which bonds to haemoglobin
    –> C = causes global dimming, respiratory issues
  • insufficient O2
24
Q

types of pollution from combustion

A
  • sulphur impurities
  • nitrogen oxides
  • greenhouse gases
25
Q

sulphur impurities –> SO2

(type of pollution)

A
  • found on coal
  • SO2 produced via incomplete combustion when sulfur is burnt
  • SO2 dissolves in water –> acid rain
26
Q

removing SO2

A
  • removed from waste gases in furnace via flue gas desulphurisation
  • gases pass through scrubber with basic CaO –> reacts with acidic SO2 in neutralisation reaction
27
Q

what is the product of flue gas desulphurisation?

(& it’s use)

A

calcium sulphite –> can be further made into calcium sulphate for plasterboard

28
Q

N + O2 –> 2NO

A
  • high temp and spark in car engine provides sufficient emergy to break strong N2 bond
  • reacts with oxygen –> prod. nitrogen oxides
  • dissolves in water –> acid rain
29
Q

what do catalytic converters do?

A
  • remove carbon monoxide, nitrogen oxides & unburned hydrocarbons –> convert them into harmless gases
  • has ceramic honeycomb coated with thin layer of catalyst metals –> gives large S.A
30
Q

identify a catalyst in the converter

A

palladium, platinum

31
Q

why is UV light needed for the synthesis of chloroalkanes?

A

UV light supplies energy to break the Cl-Cl bond

32
Q

what is the process of breaking the bonds during initiation called?

A

homolytic fission

33
Q

free radical mechanism

(steps)

A
  1. initiation -> split halogen into free radicals
  2. propagation -> extract H from alkane
  3. propagation -> replace H in free radical alkane with halogen from diatomic molecule
  4. termination -> two radicals prod. stable molecule

chemistry!👩🏽‍🔬🧪 (11 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions