3.2 Alkanes Flashcards
What is an alkane ?
A saturated hydrocarbon containing only carbon-hydrogen bonds.
What is the general formula of an alkane?
CnH2n+2.
Do alkenes have polar bonds ? Why / why not ?
They don’t, this is because they have similar electronegativities.
What intermolecular forces do alkanes have ? Why ?
They only have van der waals, they are non polar.
Are alkanes soluble in water ?
They are insoluble because the hydrogen bonds in water are stronger than alkanes’ van der waals forces.
How reactive are alkanes ?
Very unreactive.
Which reactions will alkanes undergo ?
Combustion and reactions with halogens.
What is crude oil? Is it renewable?
•It is a mixture of fractions (hydrocarbons with different boiling points)
•They are formed from biological matter at high temperatures of pressure over millions of years - unrenewable.
What is fractional distillation and how does it work with crude oil ?
•Crude oil is heated until mostly vaporised
•It is then passed into a fractionating column (cooler at top)
•Vapours rise up the column and condense when temperature < their bp
•Shorter chains will condense at the top as their bp is lowest.
Why are alkanes cracked ?
Long chain alkenes can be cracked into a shorter chain alkane and shorter chain alkene, which are both more valuable.
What are the conditions for thermal cracking ?
700-1200K
Up to 7000kPa.
What is the intermediate for the thermal cracking ?
Free radicals.
What are the main products of thermal cracking ?
Shorter chain alkenes.
What are the conditions for catalytic cracking?
Lower temp (720K)
Lower pressure but higher than atmospheric
Zeolite catalyst with a honeycomb structure for high SA.
What are the main products of catalytic cracking ?
Cycloalkanes, aromatic hydrocarbons and branched alkanes.