Organic 1: Alkanes Flashcards
what is an alkane
a saturated hydrocarbon
what is the general formula of an alkane?
Cn H2n+2
are the bonds in alkanes polar?
non-polar
carbon and hydrogen have similar electronegativities
what intermolecular forces are in alkanes and why
only van der waals - bonds are non-polar
are alkanes soluble in water
insoluble because hydrogen bonds in water are stronger than alkanes’ van der waals forces of attraction
how reactive are alkanes
very unreactive
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
- non renewable
name the fractions from high to low boiling point
- gases
- gasoline/petrol/naphtha
- kerosene/paraffin
- diesel oil
- lubricating oil/waxes
- fuel oil
- tar/bitumen
what is fractional distillation and how does it work?
- crude oil is heated until mostly vaporised
- passed into a fractionating tower that is cooler at the tip than the bottom
- liquid fractions are piped off at the bottom
- vapours rise up the column and (via trays and bubble caps) condense when the temperature is lower than 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 in 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
advantages and disadvantages 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, which is not very economically valuable, into a shorter chain alkane (more economically valuable because it can be used as a fuel) and an alkane (more reactive starting point for many products)
what are the conditions for thermal cracking?
700-1200K 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