12 Alkanes Flashcards
(37 cards)
what are alkanes
they are saturated hydrocarbons
what are hydrocarbons
compounds that only have carbon and hydrogen atoms
why are alkanes almost non polar
electronegativity of carbon and hydrogen are very similar
why does the boling points of alkanes increase with chain length
increasing the chain length would mean there are more electrons and the molecule ius getting bigger and so the strength of the van der waals forces increase requiriing more and more nergy to break the intermolecular force as the chain length increases
why are alkanes insoluble
water molecules are held by strong hydrogen bonds which are much stroner than the van der waals forces that act between the alkane molecules
why are alkanes realtively uncreactive
the c-c and the c-h bonds are very strong
what is petroleum
mixture consisting mainly of alkane hydrocarbons that can be separated by fractional distillation.
what is the fancy name of petroleum
crude oil
explain how fractional distillation is used to sperate crude oil
the crude oil is heated in a furnace
the vaporised crude oilfoes into fractionatingf colunms and rises up through the trays.Largest hydrocarbons dont vaporise due its high boiling point and they run to the bottom and collected as residue
the crude oil vapour goes up the fractionating column it gets cooler
as the alkane molecules have different chain lengths lengths they have different boiling points and so the frcations condense at different temperatures and diffrent levels
the hydrocarbons with the lowest boiling points dont condense they are drawn off as gases at the top mof the column
what is cracking
the process that breaks some bonds in long chain alkanes
describe the conditionas and products of catalytic craking
uses a zeolite catalyst low tempertaure(720K) and low pressure (just above atmospehric pressure
the products are mainly branched alkanes,cyclohexanes and aromatic compouyndss
describe the conditions and products of thermal cracking
high temperature(700-1200K) high pressure(7000kPa) produces alkenes
give an economic reason for cracking
to produce substances whihc are more in demand and have a high value
compare ctalytic cracking with thermal cracking
catalytic process more efficent and produces more branched chain molecules than thermal cracking.Branched hydrocarbons burn moe easily and are more useful as fuels.They make better petrol as they dont cause so many probelms in the car engine as they have less sulfur content.They also require less energy for temperature and pressure which decreases costs
catalytic cracking cant be used for very long hydrocarbons because they dont fit into the zeolite whereas thermal cracking can be used for very long hydrocarbons
how does the products of complete combustion differ from the products of incomplete combustion
complete produces carbon dioxide and water
incomplete produces carbon monoxide and water
when does incomplete combustion happen
when there is limited supply of oxygen
when does complete combustion happen
when there is a plentifulk supply of oxygen
what is a fuel and give an example
a substance that release heat energy when they undergo combustion and also store a large amount of energy for a msall amount of wieght eg.alkanes
how is carbon monoxide harmful
when its breathed in it combines with haemoglobin in your blood stream.The blood is no longer able to carry oxygen this lack of oxygen causes body and tissue cells to fail and die
how are nitrogen oxides harmful
they conribute to acid rain ad phtochemical smog
how does nitrogen oxides and sulfur dioxide contribute to acid rain
they combine with water in the air to form sulfiruc acid/nitric acid and tehy contribute to acid rain
how are carbon particulates harmful
when breathed in they can worsen asthma and cause cancer
how are unburnt hydrocarbons harmful
may enter atmosphere can contribute to greenhouse effect and photochemical smog which creates health problems
how is carbon dioxide harmful
they always produce hydrocarbons and is a greeenhouse gas
its rising level contributes to earths temperature to increase and consequent climate change
