Alkanes Flashcards
What is an alkane?
A saturated hydrocarbons
containing C-H bonds only
What is the general formula
of an alkane?
Cn H2n+2
Are their bonds polar?
Why/why not?
Nonpolar- carbon and
hydrogen have similar
electronegativities
Which intermolecular forces
do they have? Why?
Only van der Waals forces of
attraction - bonds are
non-polar
Are they soluble in water?
why?
Insoluble because hydrogen bonds in
water are stronger than alkanes’ van der
Waals forces of attraction
Which reactions will alkanes
undergo?
Combustion and reaction with
halogens
What is crude oil? How is it
formed? Is it renewable?
Why?
Mixture of fractions (hydrocarbons with similar
boiling points and properties)
Formed at high temperatures and pressures deep
below earth’s surface over millions of years →
therefore non-renewable
How reactive are alkanes?
Very unreactive
Name the fractions from
high to low boiling point.
Gases - fuel on site
Gasoline/petrol/naphtha - cars
Kerosene/paraffin - jet fuel, lighting
Diesel oil - lorries/taxis
Lubricating oil/waxes - candles, engine oil
Fuel oil - ships, power stations
Tar/bitumen - roads/roofing
https://bit.ly/pmt-ed
What is fractional
distillation/how does it
work?
Crude oil heated until mostly vapourised
Passed into a fractionating tower that is cooler at the top than the bottom
Liquid fractions are piped off at the bottom
Vapours rise up the column and - via trays and bubble caps - condense
when temperature < their boiling point
Shortest chain hydrocarbons condense at the top as they have the lowest
boiling points
What is fracking and how is
it done?
Natural gas held within shale rock
Drill into shale, force pressurised water and sand into rock to
fracture it, Collect gas
HCl and methanol added to break up shale and prevent
corrosion
Pros/cons of fracking?
Advantages - gas supply for many years, reduces imported
gas and electricity
Disadvantages - lots of traffic to local area, concern about
amount of water used, chemical additives can pollute water
supplies, can cause small earthquakes, combust CH4 → CO2
→ global warming
Why are alkanes cracked?
To turn a long chain alkane, with is not very
economically valuable, into a shorter chain
alkane (more economically valuable as can be
used as a fuel) and an alkene (more reactive,
starting point for many products)
What are the conditions for
thermal cracking?
700-1200 K temperature
Up to 7000 kPa pressure
What is the intermediate for
the reaction?
Free radicals
What are the main products
of thermal cracking?
alkenes
What are the conditions for
catalytic cracking?
Lower temp (720K)
Lower pressure (but above atmospheric)
Zeolite catalyst (SiO2 and Al2O3) with a
honeycomb structure to give a large surface area
What are the main products
of catalytic cracking?
Cycloalkanes, aromatic hydrocarbons,
branched alkanes
Write an equation for the
combustion of propane
C3H8
+ 5O2 → 3CO2 + 4H2O
What is a fuel?
Something which releases heat energy
when combusted
What are the five main fuels
comprising of alkanes?
Methane, butane, propane, petrol (about
C8), paraffin (C10 - C18)
What is incomplete
combustion and what
products are formed in the
case of alkanes?
Combustion in a limited supply of oxygen
CO - carbon monoxide - poisonous
C - carbon - particulates - soot - global dimming
Which type of hydrocarbons
are most likely to undergo
incomplete combustion?
Longer chains
What is the environmental
impact of carbon monoxide?
It is toxic/poisonous
