alkanes and alkenes Flashcards
define alkanes
contain carbon-carbon single bonds only
aka saturated hydrocarbons
define alkenes
contain one or more carbon-carbon double bonds
aka unsaturated hydrocarbons
alkanes general formula
CnH2n+2
alkenes general formula
CnH2n
what are the physical trends for both alkene and alkane as we go down the series
melting and boiling increases
viscosity increases
density increases
flammability decreases
name all the alkanes and its formula
methane CH4 ethane C2H6 propane C3H8 butane C4H10 pentane C5H12 hexane C6H14
name all the alkenes and its formula
ethene C2H4 propene C3H6 butene C4H8 pentene C5H10 hexeneC6H12
what are the chemical reactions in alkanes
combustion
substitution with halogens
cracking of long chain alkanes
what are the chemical reactions in alkenes
combustion
addition reactions
producing alkenes by cracking
what is complete combustion
when there is sufficient oxygen supply
what is the equation of combustion in alkanes
alkane + oxygen –> carbon dioxide + water vapour
what is the equation of combustion in alkenes
alkene + oxygen –> carbon dioxide + water vapour
what is the reagent in substitution with halogens
halogens
what is the condition required in substitution with halogens
ultraviolet (UV) light
what happens in each stage of substitution with halogens
at each stage, 1 halogen replace 1 hydrogen atom
HCL (hydrogen chloride gas) is produced at each stage as a by-product
what are the 2 addition reactions that alkene can take place
hydrogen and
aqueous bromine
what are the conditions required in addition reactions with hydrogen
200 degree celcius and
catalyst, nickel
what is the chemical equation of addition reactions with hydrogen
alkene + hydrogen gas –> alknes
alkene + hydrogen gas –> alknes
what does this process called?
hydrogenation
what is hydrogenation
when vege oil (unsaturated hydrocarbons) is hydrogenated it is converted into solid margarine (saturated hydrocarbons)
what is the chemical equation of addition reactions with aqueous bromine
alkene + Br2 –> bromoalkene
how to know if the results are alkenes or alkanes in addition reactions with aqueous bromine
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
what is cracking of long chain alkanes / producing alkenes by cracking
it is the breakdown of long chain alkane hydrocarbon to produce smaller, useful molecules
what are the conditions required in cracking of long chain alkanes / producing alkenes by cracking
high temperatures (abt 600 degree celcius) catalyst, silicon dioxide or aluminium oxide
what are the 2 possible chemical equations of cracking of long chain alkanes / producing alkenes by cracking
large alkane –> smaller alkane + alkene
large alkane –> alkenes + hydrogen gas
give 3 similarities between alkanes and alkenes
both are hydrocarbons
flammable
produce carbon dioxide and hydrogen gas, on complete combustion
give 3 differences between alkanes and alkenes
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
define polyunsaturated
many c-c double bonds
what is incomplete combustion
where there is limited/ insufficient supply of oxygen
what is the general word equation of incomplete combustion for alkane and alkene
alkane/ alkene + oxygen –> mixture of carbon dioxide, carbon monoxide, soot + water vapour
