organic chemistry Flashcards
what resource is crude oil and where is it found
a finite resource found in rocks
what is crude oil
the remains of an ancient biomass consisting mainly of plankton that was buried in mud
what is crude oil a mixture of
a very large number of compounds, mostly hydrocarbons
what are hydrocarbons
molecules made up of hydrogen and carbon atoms only
general formula for homologous series of alkanes
CₙH₂ₙ₊₂
first four alkanes
Mouses Eat Peanut Butter
Methane, Ethane, Propane, Butane
define a homologous series
a series of hydrocarbons with similar properties and that react in a similar way
what compounds are alkanes and why
saturated compounds because they have no double bonds (all of its electrons are being used for bonding)
what type of bonding is in hydrocarbons
covalent, because both atoms are non-metals (hydrogen and carbon)
what can the hydrocarbons in crude oil be separated into
fractions, each of which contains molecules with a similar number of carbon atoms, by fractional distillation
what can the fractions be processed to produce
fuels and feedstock for the petrochemical industry
what oils are produced from crude oil (in order from top to bottom of fractional column)
many of the fuels on which we depend for our modern lifestyle, e.g., liquefied petroleum gases (camping stoves), petrol (cars), kerosene (jet fuel), diesel oil (larger cars and vans) and heavy fuel oil (ships)
what is produced by the petrochemical industry
many useful materials on which modern life depends, such as solvents, lubricants, detergents and polymers
why is there a vast array of natural and synthetic carbon compounds
due to the ability of carbon atoms to form families of similar compounds
why do we separate the different hydrocarbons in crude oil
because they all contain different properties useful for different purposes - crude oil without separation is useless
method for separating crude oil
fractional distillation
1) heat crude oil until becomes vapour and feed it into fractionating column - hot at bottom, cooler at top
2) each fraction of hydrocarbon gases within the vapour condense into liquid at different points along the fractionating column bc they all have different boiling points so will condense at different temps
3) this separates the crude oil into diff fractions, each with similar number of carbon atoms
4) longer chain hydrocarbons have higher boiling points bc larger molecule so condense into liquid at bottom of column, while shorter chain hydrocarbons have lower boiling points so condense at top of column - some won’t condense at all and will remain gas, producing LPG (liquified petroleum gas)
factors affecting properties of hydrocarbons
size of molecules:
- boiling point
- viscosity
- flammability
how does fractional distillation for crude oil work
each fraction of hydrocarbons has diff boiling point so condenses at diff heights of column
how does viscosity affect properties of hydrocarbons
more viscous fluid flows more slowly
- as size of hydrocarbon molec increases, viscosity increases
TO HELP REMEMBER (dont say in exam)
- bigger = more intermolecular forces so stick together and more viscous
how does flammability affect properties of hydrocarbons
tells us how easily hydrocarbon combusts
- as size of hydrocarbon molec increases, flammability decreases, so short chain hydrocarbons v flammable
TO HELP REMEMBER
methane is main component in natural gas used to heat homes - high flammability, short chain hydrocarbon
how does boiling point affect properties of hydrocarbons
temperature when liquid -> gas
- as size of hydrocarbon increases, boiling point increases, so short chain hydrocarbons are gases at room temp
TO HELP REMEMBER
methane is gas so very low boiling point
what does the combustion of hydrocarbon fuels release
energy
what happens during combustion of hydrocarbons
the carbon and hydrogen in the fuels are oxidised, because the hydrogen is combining with oxygen to form water and the carbon is combining with the oxygen to form carbon dioxide
equation for complete combustion of a hydrocarbon
hydrocarbon + oxygen -> carbon dioxide + water
what type of reaction is complete combustion
exothermic as lots of energy is released in the process
what is cracking
hydrocarbons being broken down to produce smaller, more useful molecules
why is cracking important
long-chain hydrocarbons tend to have much lower demand, as they are less flammable than short-chain so less effective as fuels
what is the issue with high demand for short-chain hydrocarbons and how is this resolved
most hydrocarbons found in crude oil are long-chain - so to meet demand and produce more useful molecule, they undergo cracking
two methods used for cracking
- catalytic cracking; high temp and catalyst
- steam cracking; high temp and steam
what is catalytic cracking
we pass the hydrocarbon vapour over a hot catalyst causing the long-chain hydrocarbon to split into two or more shorter hydrocarbons
what is steam cracking
we mix the hydrocarbon vapour with steam and heat it to a very high temperature in order to split it into two or more shorter hydrocarbons
what is the difference between alkanes and alkenes
alkenes have a double bond (C=C) whereas alkanes only have single bonds - this means alkanes are saturated whereas alkenes are unsaturated molecules
why are alkenes more reactive than alkanes
alkenes are unsaturated, meaning this double bond can open up and bond to 2 other atoms, making it more reactive
what are the products of cracking
alkanes and alkenes
what do alkenes react with
bromine water
what is the positive test for alkenes
adding bromine water to a solution - if it turns from orange to colourless, alkenes are present
why does bromine water remain orange in the presence of alkanes
alkanes are saturated so cannot react with bromine
what are alkenes used for
- to produce polymers
- as starting materials for the production of many other chemicals