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z-chemistry > alkanes and alkenes > Flashcards

alkanes and alkenes Flashcards

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1
Q

define alkanes

A

contain carbon-carbon single bonds only

aka saturated hydrocarbons

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2
Q

define alkenes

A

contain one or more carbon-carbon double bonds

aka unsaturated hydrocarbons

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3
Q

alkanes general formula

A

CnH2n+2

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4
Q

alkenes general formula

A

CnH2n

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5
Q

what are the physical trends for both alkene and alkane as we go down the series

A

melting and boiling increases
viscosity increases
density increases
flammability decreases

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6
Q

name all the alkanes and its formula

A 
methane CH4
ethane C2H6
propane C3H8
butane C4H10
pentane C5H12
hexane C6H14
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7
Q

name all the alkenes and its formula

A 
ethene C2H4
propene C3H6
butene C4H8
pentene C5H10
hexeneC6H12
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8
Q

what are the chemical reactions in alkanes

A

combustion
substitution with halogens
cracking of long chain alkanes

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9
Q

what are the chemical reactions in alkenes

A

combustion
addition reactions
producing alkenes by cracking

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10
Q

what is complete combustion

A

when there is sufficient oxygen supply

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11
Q

what is the equation of combustion in alkanes

A

alkane + oxygen –> carbon dioxide + water vapour

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12
Q

what is the equation of combustion in alkenes

A

alkene + oxygen –> carbon dioxide + water vapour

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13
Q

what is the reagent in substitution with halogens

A

halogens

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14
Q

what is the condition required in substitution with halogens

A

ultraviolet (UV) light

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15
Q

what happens in each stage of substitution with halogens

A

at each stage, 1 halogen replace 1 hydrogen atom

HCL (hydrogen chloride gas) is produced at each stage as a by-product

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16
Q

what are the 2 addition reactions that alkene can take place

A

hydrogen and

aqueous bromine

17
Q

what are the conditions required in addition reactions with hydrogen

A

200 degree celcius and

catalyst, nickel

18
Q

what is the chemical equation of addition reactions with hydrogen

A

alkene + hydrogen gas –> alknes

19
Q

alkene + hydrogen gas –> alknes

what does this process called?

A

hydrogenation

20
Q

what is hydrogenation

A

when vege oil (unsaturated hydrocarbons) is hydrogenated it is converted into solid margarine (saturated hydrocarbons)

21
Q

what is the chemical equation of addition reactions with aqueous bromine

A

alkene + Br2 –> bromoalkene

22
Q

how to know if the results are alkenes or alkanes in addition reactions with aqueous bromine

A

add few drops of reddish-brown aqueous bromine
result:
alkane- if it does not react with the reddish-brown aqueous bromine
alkene- it decolourises the reddish-brown aqueous bromine

23
Q

what is cracking of long chain alkanes / producing alkenes by cracking

A

it is the breakdown of long chain alkane hydrocarbon to produce smaller, useful molecules

24
Q

what are the conditions required in cracking of long chain alkanes / producing alkenes by cracking

A 
high temperatures (abt 600 degree celcius) 
catalyst, silicon dioxide or aluminium oxide
25
Q

what are the 2 possible chemical equations of cracking of long chain alkanes / producing alkenes by cracking

A

large alkane –> smaller alkane + alkene

large alkane –> alkenes + hydrogen gas

26
Q

give 3 similarities between alkanes and alkenes

A

both are hydrocarbons
flammable
produce carbon dioxide and hydrogen gas, on complete combustion

27
Q

give 3 differences between alkanes and alkenes

A 
alkane:
c-c single bonds only 
unreactive
undergo substitution with halogens 
do not react with Br2
reacts very slowly in the presence of UV light 
alkene:
1 or more c-c double bonds 
reactive 
undergoes addition reaction 
rapidly decolourises Br2
28
Q

define polyunsaturated

A

many c-c double bonds

29
Q

what is incomplete combustion

A

where there is limited/ insufficient supply of oxygen

30
Q

what is the general word equation of incomplete combustion for alkane and alkene

A

alkane/ alkene + oxygen –> mixture of carbon dioxide, carbon monoxide, soot + water vapour

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