Alkanes Flashcards
alkanes are?
saturated hydrocarbons
what is petroleum?
crude oil; mixture consisting of alkane hydrocarbons that can be separated by fractional distillation
what is crude oil?
fossil fuel made from breakdown of plant and animal remains subjected to high pressure over millions of years
why are alkanes non polar
electronegativaties of hydrogen and carbon are so similar
forces between alkanes
VDW
why do alkanes with branched chains have lower boiling points than unbranched ones w/ the same number of hydrocarbons
cannot pack closely together- weaker VDW
why are alkanes insoluble in water
water held by hydrogen bonds stronger than VDW forces in alkanes
but alkanes do mix w/ other non-polar liquids
what does cracking involve
breaking C-C bonds in alkanes
petrol is?
mixture of mainly alkanes w/ 4-12 carbons
alkenes are?
used as chemical feedstock, and are converted to polymers, pains, drugs
thermal cracking
- high pressure (up to 7000kPa)
- high temp (700-1200°K)
- produces high % of alkenes
catalytic cracking
- high temp
- slight pressure (just more than atmospheric pressure)
- zeolite catalyst
- used mainly to produce motor fuels + aromatic hydrocarbons
- zeolite: silicone dioxide and aluminium oxide
- products are mostly branched alkanes cycloalkanes, aromatic compounds
internal combustion in an engine
produces large no. of pollutants, including NOx, CO, carbon and unburnt hydrocarbons
complete combustion
alkane+oxygen -> carbon dioxide+water
gives out heat; exothermic
store lots of energy in small weight
burns w/ a blue flame
incomplete combustion
alkane+oxygen -> carbon monoxide+water
carbon monoxide or carbon (soot) produced in limited oxygen supply
often happens w/ long chained hydrocarbons- need more O2 than short chain
burns w/ dirty yellow flame
what are catalytic converters
remove gaseous pollutants from internal combustion engines
how do catalytic converters work
use precious metals to spread over mesh; honeycomb structure to increase s.a. so less expensive metal is needed. used as catalysts i think?
what do catalytic converters do
reduce output of CO, NOx, unburnt hydrocarbons, forms N2, CO2, H2O
CO2
greenhouse gas, climate change
CO
incomplete combustion, poisonous
NOx
enough energy for N2 and O2 in air to combine, may react w/ water vapour and O2 in air to form nitric acid; acid rain and photochemical smog
sulfur dioxide
acid rain, produced when there are sulfur containing impurities in hydrocarbons.
carbon particulates
asthma + cause cancer
unburnt hydrocarbons
enter atmosphere, greenhouse effect, photochemical smog, health problems
