Chapter 12 - Alkanes
No description yet. This curated deck is ready for daily study.
Card preview (24)
what are alkanes
a holologous series of saturated hydrocarbons with the general formula CnH2n+2 they are very unreactive, aside from burning and reacting with halogens
describe and explain the trend in boiling points as the carbon chain increases in length comment on branched isomers
they generally increase as the chain increases because the strength of van der waals forces in between molecules increase as the total number of electrons increases. for chained isomers, the more branches there are, the lower the boiling point because the molecules cannot pack as close togehter resulting in lower van der waals forces
what is crude oil and how is it formed
crude oils are fossil fuels containing a mixture of hydrocarbons they are formed during the slow decay of marine organisms over millions of years in high heat, high pressure, and anaerobic conditions
on what basis are compound separated in fractional distilation
different length chains have different boiling points so we can separate these using fractional distillation
how is fractional distillation carries out
crude oil is vaporided the vapour is passes into a tower which is cold at the top and hot at the bottom as the vapour rises, it cools different length molecules will condense at different heights (shorter at top, longer at bottom)
what is cracking
the breaking of c-c bonds in long hydrocarbons to make shorter hydrocarbons which are more in demand it is the thermal decomposition of alkanes
what are the conditions of thermal cracking
900 Celsius 70atm no catalyst produces alkenes used for polymers for example
what are the conditions and products of catalytic cracking
450 Celsius 1-2 atm zeolite catalysts produces motor fuels (aromatics, cyclic alkanes, branched alkanes)
what is reforming and why is it used
a process where straight chain hydrocarbons are converted into branched chain alkanes and cyclic alkanes. Both these products burn more efficiently and are used in petrol for cars.
why are alkanes useful as fuels
because when burned in the presence of oxygen, the reaction is highly exothermic
what are the products of complete alkane combustion
carbon dioxide and water
what are the products of incomplete alkane combustion
either carbon monoxide and water or carbon and water
when does incomplete combustion occur
when there is not enough oxygen
how is CO2 formed, what problem does it cause, and how can you reduce this
complete combustion of carbon based fuels it is a greenhouse gas burn less fossil fuels
how is CO formed, what problem does it cause, and how can you reduce this
incomplete combustion of carbon based fuels it is highly toxic ensure a good supply of oxygen when burning fuels
how is soot formed, what problem does it cause, and how can you reduce this
incomplete combustion of carbon based fuels global dimming, respiratory problems, blackens buildings ensure a good supply of oxygen when burning fuels
how is H2O formed, what problem does it cause, and how can you reduce this
combustion of fuels containing hydrogen it isnt a major problem
how is SO2 formed, what problem does it cause, and how can you reduce this
combustion of sulfur compounds in fuels acid rain remove sulfur from fuel before burning, use flue gas desulfurisation
how are nitrate oxides (NOx) formed, what problem does it cause, and how can you reduce this
reaction of N2 in the air with O2 in the air at very high temperatures acid rain use catalytic converter (in cars)
how are unburned hydrocarbons formed, what problem does it cause, and how can you reduce this
some fuel just doesnt burn/react this is a waste of fuel ensure all engines are well tuned and have a good oxygen supply
how can you remove SO2 from waste gases produced in fuel combustion
using flue gas desulfurisation this involves passing the gases through a scrubber containing calcium oxide or calcium carbonate which reacts with the SO2 to form CaSO3 (gypsum) which can be used to make plasterboard
what do catalytic converters do
they remove CO2, NOx and unburned hydrocarbons, turning them into CO2, NOx, and H2O
CHECK THIS how do greenhouse gases work
They absorb infrared radiation emitted by the Earth – this is due to bond vibrations (these vibrations lead to changes in dipoles that lead to the absorption of infrared).
state a condition necessary for free radical mechanism reactions
the presence of UV rays