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- Created by: elisha.ks
- Created on: 07-03-17 19:22
what is crude oil
a mixture of a very large number of compounds (that aren't chemically bonded to each other)
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what is a mixture
consists of two or more elements or compounds not chemically combined together
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what is special about a mixture and what does this allow
chemical properties of each substance in the mixture are unchanged. It is possible to separate the substances in a mixture by physical methods including distillation
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what do most of the compounds in crude oil consist of
molecules made up of hydrogen and carbon atoms only (hydrocarbons)
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what are most of these hydrocarbons
saturated hydrocarbons called alkanes
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formula for alkanes
C
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structure of alkane molecules
carbon atoms form 4 bonds, hydrogen atoms form 1 bond, all covalent, all make maximum no. of bonds so are saturated
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what are the first four alkanes, their formulae and structures
methane(natural gas), ethane, propane, butane
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what do some properties of hydrocarbons depend on and what does this affect
the size of their molecules - influences how hydrocarbons are used as fuels
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the shorter the molecules...
the less viscous, more flammable, more volatile (lower boiling point so fraction vaporises or condenses at lower temp.)
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how does fractional distillation work
hydrocarbons in crude oil may be separated into fractions, each of which contains molecules with a similar number of carbon atoms
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processes in fractionating column
continuos fractional distillation: evaporating the oil so it rises and allowing it to condense at a number of different temperatures for various fractions
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why is crude oil an important fuel
burns cleanly so makes good fuel, most transport fuelled by a fraction, some burned in central heating systems in homes and power stations to generate electricity,
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other uses for crude oil
raw material for making chemicals, including plastics
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positives of crude oil
readily available as petrol, easiest+cheapest to use, more reliable than solar or wind power
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negatives of crude oil
non-renewable fuel, oil spills as it's transported so animals poisoned, has to be burnt so bad for environment
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what do power stations do
burn huge amounts of fossil fuels to make electricity
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what do most fuels contain
carbon and/or hydrogen and may also contain some sulfur
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what happens during combustion
(of hydrocarbon fuels) carbon and hydrogen in the fuels are oxidised and energy is released
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hydrocarbon + oxygen =
carbon dioxide + water vapour
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what is complete combustion
when there's plenty of oxygen so all the fuel burns
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what is partial combustion and what is released from this
not enough oxygen so some of the fuel doesnt burn: solid particles (particulates) and carbon monoxide
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what might particulates contain
soot (carbon) and unburnt fuels
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what's released if the fuel contains sulfur impurities
sulfur dioxide
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what happens if the fuel burns at a high temperature
oxides of nitrogen form
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what can sulfur dioxide and oxides of nitrogen cause
acid rain as it mixes with clouds to form dilute nitric/sulfuric acid
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what can acid rain cause
lakes become acidic so animals/plants die, kills trees, damages limestone buildings
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how can sulfur emissions be reduced
sulfur removed from fuels before they're burnt (in vechiles), Sulfur dioxide can be removed from the waste gases after combustion (in power stations), reduce use of fossil fuels
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what does carbom dioxide cause
global warming: climate change, levels in atmosphere are increasing cus large amounts of fossil fuels burned, can cause severe flooding due to ice caps melting
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what do solid particles cause
global dimming: less sunlight reaches earth's surface cus particles reflect sunlight or can help produce more clouds
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what's being developed (3 examples)
alternative fuels, most are renewable so won't run out like fossil fuels
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what is ethanol
produced from plant material (biofuel), made by fermentation of plants and used to power some cars, often mixed with petrol
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pros/cons of ethanol
carbon neutral as CO2 released when burnt is taken in by plant and only product is water/ engines need to be converted to work w fuel and isnt widely available, more crops to grow ethanol instead means less food so increase food prices
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what is biodiesal
(biofuel) produced from vegetable oils like rapeseed oil, can be mixed with ordinary to run diesel engine
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pros/cons of biodiesal
carbon neutral, engines dont need converting, produces less sulfur dioxide+particulates/ expensive to make, cant make enough to replace all diesel, increase food prices like ethanol
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what is hydrogen gas
used to power vehicles, get hydrogen from electrolysis of water, requires electrical energy which can come from renable source
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pros/cons of hydrogen gas
combines w oxygen in air to form water so v clean/ need special, expensive engine, isnt widely available, still need energy from another source, hard to store
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Other cards in this set
Card 2
Front
what is a mixture
Back
consists of two or more elements or compounds not chemically combined together
Card 3
Front
what is special about a mixture and what does this allow
Back
Card 4
Front
what do most of the compounds in crude oil consist of
Back
Card 5
Front
what are most of these hydrocarbons
Back
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