alkanes
No description yet. This curated deck is ready for daily study.
Card preview (24)
why are alkane molecules non-polar?
C and H have very similar electronegativities so form non-polar bonds
how are neighbouring alkane molecules attached to each other?
by Van Der Waals’ forces- weak intermolecular forces
describe alkane solubility in water?
hydrogen bonds between water molecules are much stronger than the Van Der Waals’ in alkanes so they are insoluble in water
the longer the carbon chain the…..
higher the bp higher the viscosity lower the flammability
why does the bp increase for longer chain alkanes?
-more SA (only talk about this for straight chains not branched) -larger molecule -greater number of electrons SO more and stronger VDW forces between molecules = more energy to overcome
what is the general formula for alkanes?
Cn H2n+2
what is a hydrocarbon?
a compound containing hydrogen and carbon atoms only
are alkanes saturated or unsaturated, why?
saturated only single bonds between carbon atoms
what is the general formula for cycloalkanes?
Cn H2n
what is crude oil/ petroleum?
a mixture consisting mainly of alkane hydrocarbons and it is our main source of fuels and petrochemicals
what is a mixture?
more than one different compounds or elements not chemically bonded together
what is fractional distillation?
the separation of the components of a liquid into fractions which differ in boiling points
what is a fraction?
a mixture of compounds that have similar boiling points and are removed at the same level in the fractionating column
explain why branched alkanes have a lower boiling point?
more branched means less SA which means there are less points of contact where VDW’s can form less VDW formed and weaker VDW = less energy to overcome
when can we only use the assumption that branched alkanes have a lower boiling point?
when they have a similar Mr and so are similar in size
describe the process of fractional distillation?
-vaporise crude oil in the furnace so the vapor can rise up the column -the top of the column is cooler than the bottom -larger, longer hydrocarbons condense at the bottom of the column, shorter, smaller hydrocarbons condense at the top of the column
which two fractions don’t vaporise or condense?
bitumen has too high of a boiling point to vaporise so leaves at the bottom as a liquid petroleum gas doesn’t condense so leaves the top of the column as a gas
what are the two types of cracking?
thermal and catalytic
how is cracking achieved?
by breaking C-C bonds, producing shorter chain hydrocarbons from longer chain hydrocarbons
why do we do cracking?
we have a lower supply and higher demand for shorter hydrocarbons we have a higher supply and lower demand for longer hydrocarbons
what are the conditions for thermal cracking?
very high pressures and very high temperatures
what does thermal cracking produce?
alkanes and a high percentage of alkenes
how are mixtures of products produced in thermal cracking?
the C-C bonds can break at different positions in the carbon chain
what are the products of thermal cracking used to make?
polymers (mainly alkenes)