Alkanes Flashcards
what are alkanes
saturated hydrocarbons
what is a hydrocarbon
contains hydrogen and carbon only
what does it mean by saturated
each carbon is bonded 4 times with the maximum number of hydrogens possible
what do cycloalkanes have
2 hydrogens per carbon
saturated
functional group isomer of alkenes
where are alkanes found
in crude oil which is a mixture of different length of hydrocarbons
how is crude oil vapourised
using a furnace to 350 degrees
what does the vapourised oil do once it enters the column
it rises through the trays
the longest hydrocarbons don’t vaporise and run down to the bottom
describe the temperature gradient in a fractioning column
cooler at the top
as the vapour rises parts of the mixture condense at different temperatures
due to the different chain lengths = different bp
fractions are drawn at different levels
what happens to shortest hydrocarbons
they don’t condense at 20 degrees so come off as a gas at the top of the column
what is cracking
breaking longer chain alkane into shorter hydrocarbons
what are the two types of cracking
thermal and catalytic
what are the conditions for thermal cracking
high temperature of 1000 degrees and 70 atm pressure
what is the main products of thermal cracking
alkenes
what are alkenes used to make
polymers
e.g. plastic
what are the conditions for catalytic cracking
slight pressure
high temperature of 450 degrees
a zeolite catalyst is used to help lower the temperature needed
what are the products of catalytic cracking
aromatic hydrocarbons
useful for fuel in vehicles
what does a zeolite catalyst do
lowers temperature and pressure so cracking can occur
lowers costs and speeds up process
complete combustion of alkanes
burn in oxygen completely to form co2 and h2o
what is the incomplete combustion of alkanes
alkanes burn with a limited 02 supply it produces carbon monoxide (CO) and carbon (soot)
why is carbon monoxide dangerous
-poisonous
-it binds to haemoglobin in the blood preventing oxygen bonding
-carbon monoxide can be removed using a catalytic converter
what does burning fossil fuels do
produces co2 = greenhouse gas
what is the greenhouse effect
co2 absorbs infrared radiation (heat) from the sun
but it emits some of it back to earth = greenhouse effect
what does ozone cause
photochemical smog which harms the respiratory system
where does ozone occur
in the lowest levels of the atmosphere
exists as sunlight, hydrocarbon and nitrogen dioxide and mixes to form ozone (toxic)
when are oxides of nitrogen made
when oxygen and nitrogen are found in the air combine under high pressure and temperature
what do catalytic converters do
reduce the amount of unburnt hydrocarbons and oxides of nitrogen going into the atmosphere
what is wet scrubbing
it helps remove so2 from flue gases
this is where an alkali is used to neutralise sulphur dioxide from flue gases
what does a chain reaction involve
initiation
propagation
termination
what is initiation
radicals produced normally using visible light or ultraviolet
= photochemical reactions / photodissociation
the bond breaks equally producing 2 highly reactive radicals
what is propagation
when a radical reacts with a non radical molecule
new radicals are created and then go on to react with other non-radicals = chain reaction
what is termination
when 2 radicals react to form a stable non radical molecule
this ends the chain reaction hence termination
