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
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
toxic/poisonous
what is the environmental impact of nitrogen oxides
form nitric acid - acid rain, photochemical smog
what is the environmental impact of sulfur impurities/sulfur dioxide
form sulphuric acid –> acid rain
what is the environmental impact of soot
asthma
cancer
global dimming
what is the environmental impact of unburnt hydrocarbons
photochemical smog
what is the environmental impact of carbon dioxide
greenhouse gas mean global warming
increasing global temperatures speeds up climate change
what is the environmental impact of water vapour
greenhouse gas - global warming
increases global temperatures therefore speeds up climate change
what are flue gases
gases given out by power stations
write two equations for two different ways of desulfurising flue gases
CaO(s)+2H2O(l)+SO2(g)+1/2O2(g)–> CaSO4.2H2O(s)
or
CaCO3(s)+SO2(g)+1/2O2(g)–> CaSO4+CO2(g)
what are catalytic converters made up of
ceramic honeycomb coated with platinum, palladium and rhodium metals
what do catalytic converters catalyse (include equations)
catalyse products from car exhausts
2CO(g) + 2NO(g) –> N2(g) + 2CO2(g)
hydrocarbons+NO–> N2 + CO2 + H2O
what are greenhouse gases
gases which trap infrared radiation, making the earth act like a greenhouse
what is the greenhouse effect and how does it contribute to global warming
greenhouse gases trap infrared radiation in the atmosphere, atmosphere heats up –> global warming
define carbon neutral activities
activities that produce no net carbon dioxide emissions
how are halogenoalkanes formed from alkanes
free radical substitution reaction
what are the three stages of free radical substitution?
- initiation - breaking halogen bond to form free radicals
- propagation - chain part of the reaction where products are formed but free radical remains
- termination - free radicals removed, stable products formed
what are the conditions needed for the formation of a free radical chlorine atom?
presence of UV light
write equation for the reaction of CH4 with Cl2 to form CH3Cl
initiation - Cl2 --> 2Cl propagation Cl + CH4 -->HCl + CH3 CH3 + Cl2 --> CH3Cl + Cl termination CH3 + Cl --> CH3Cl 2Cl -->Cl2 CH3 + CH3 --> CH3CH3
what is the function of the ozone layer
protects the earth from harmful exposure to too many UV rays
how do CFCs break the ozone layer down
free radical substitution
write an equation for the overall decomposition of ozone into oxygen (o2)
2O3 –> 3O2
write the free radical substitution equations to show how Cl free radicals catalyse the decomposition of O3
Cl2 –> 2Cl (in presence of UV light)
Cl + O3 –> ClO + O2
ClO + O3 –> 2O2 + C
overall: 2O3 –> 3O2
