SC8: fuels and earth science Flashcards
hydrocarbons
compounds that only contain hydrogen and carbon atoms (covalently bonded)
crude oil
-a natural resource that is a complex mixture of hydrocarbons
-the carbon atoms in these molecules are joined together in chains and rings of different lengths, the different lengths give each chain unique properties
finite
limited
why is crude oil finite?
it forms very slowly over millions of years and can’t be quickly replaced
uses of crude oil:
-fuel (petrol, kerosene, diesel)
-heating buildings
-power stations
-raw materials for polymers
-a feedstock for the petrochemical industry
feedstock
a raw material used to provide reactants for an industrial reaction
non-renewable
being used up faster than it can be replaced
what is methane made from?
natural gas
fractional distillation
separates a liquid mixture into its individual components
how does fractional distillation work with crude oil?
- crude oil is pumped into the furnace
- the furnace is very hot, therefore the crude oil is heated up and evaporates
- the crude oil vapour moves from the furnace into the fractioning column
- the fractioning column is hot at the bottom and cool at the top
- the different vapours of hydrocarbons rise up the fractioning column & condense when it is cool enough
- at this point, they are collected as liquids
different levels of the fractioning column
- top: gases (25 degrees)
-fuel for domestic heating & cooking - petrol
-fuel for cars - kerosene
-fuel for aircraft’s - diesel oil
-fuel for some cars & trains - fuel oil
-fuel for ships & power stations - bottom: bitumen (350 degrees)
-for roads and roofs
how properties change up and down the fractioning column
top:
-small molecules
-low boiling point
-flows easily (low viscosity)
-ignites easily
bottom:
-large molecules
-high boiling point
-high viscosity
-doesn’t ignite easily
hydrocarbons with larger molecules have _____ boiling points
higher
what are fuels from crude oil or natural gas called?
fossil fuels
mnemonic for fractions
good (gas)
penguins (petrol)
keep (kerosene)
diving (diesel)
for (fuel oil)
bass (bitumen)
alkanes
-each crude oil fraction contains a mixture of hydrocarbons
-the hydrocarbons in a fraction are mostly hydrocarbons called alkanes
-an alkane is a saturated hydrocarbon containing only single covalent bonds
- homologous series
homologous series
organic compounds that have the same functional group and similar chemical properties
alkane formula
CnH2n+2
(where n stands for the number of carbon atoms)
properties of alkanes
-hydrocarbons
-can be gotten from crude oil
-single covalent bonds (saturated)
-in chains
-common formula
similarities of alkanes
-boiling points
-ease of ignition
-viscosity
why does boiling point increase as the number of carbon atoms increases:
-the intermolecular forces between alkane molecules become stronger, more energy is needed to overcome these forces, the boiling point increases
alkanes as a homologous series
-same general formula
-gradual variation in physical
properties
-have similar chemical properties
-differ by CH2 in the molecular formula of neighbouring compound
how prefixes correlate to amounts of carbon
meth = 1
eth = 2
prop = 3
but = 4
pent = 5
hex = 6
hept = 7
oct = 8
non = 9
dec = 10
combustion of hydrocarbon fuels
hydrocarbonfuels can undergo complete combustion or incomplete combustion, depending on the amount of oxygen available
complete combustion of hydrocarbons
-happens when there is a good supply of air
-carbon and hydrogen atoms in the fuel react with oxygen in an exothermic reaction
-maximum energy given out
(hydrocarbon + oxygen → carbon dioxide + water)
incomplete combustion of hydrocarbon fuels
-happens when the supply of air or oxygen is poor
-water is still produced, but carbon monoxide and carbon are also produced
-less energy is released than during complete combustion
(hydrocarbon + oxygen → carbon monoxide + carbon + water)
soot description (combustion of hydrocarbons)
carbon is released as fine black particles
problems with soot
-can cause breathing problems & blackens building
-may block boilers and other appliances, or cause a fire
carbon monoxide (incomplete combustion of hydrocarbons)
colourless, odorless, and toxic gas
complications of carbon monoxide
-it is absorbed in the lungs and binds with the haemoglobin in the red blood cells
-this reduces the capacity of the blood to carry oxygen
-causes drowsiness, and affected people may fall unconscious or even die
what pollutants can be formed by hydrocarbon combustion?
carbon, soot, sulfur dioxide & oxides of nitrogen
sulfur dioxide (incomplete combustion of hydrocarbons)
-many hydrocarbon fuels naturally contain sulfur impurities
-when the fuels are burned, the sulfur oxidises to form sulfur dioxide gas
formation of acid rain
-sulfur dioxide (from combustion of carbons) dissolves in water in clouds to form sulfurous acid
-oxygen in the air reacts with sulfurous acid to form sulfuric acid
-the mixture of the two acids falls from the clouds as acid rain
effects of acid rain
-reacts with metals and rocks, weakening and damaging buildings and statues
-damages plants and trees, making them lose their leaves and die
-makes rivers and lakes too acidic for some aquatic life to survive
formation of oxides of nitrogen
-high temperatures are reached when fuels are burned in engines, at these high temperatures, nitrogen and oxygen from the air can react together to produce oxides of nitrogen
nitrogen + oxygen → nitrogen monoxide
-nitrogen monoxide gas can be oxidised further in air to produce nitrogen dioxide gas
-these two oxides of nitrogen are together represented by the formula NOx
how do oxides of nitrogen react with sunlight?
they produce a hazy, toxic smog
complications of nitrogen dioxide
-can cause bronchitis & other lung diseases
cracking
larger hydrocarbon molecules are broken down into smaller, more useful hydrocarbon molecules
what does cracking form?
-the original starting hydrocarbons are alkanes
-the products of cracking include alkanes and alkenes, members of a different homologous series
alkenes
unsaturated hydrocarbons with a double bond between the carbon atoms
products of cracking of hexane
forms butane & ethane
steps of cracking
-the larger alkanes are heated to around 650°C and their vapours are passed over a hot catalyst containing aluminium oxide
-this causes covalent bonds to break and reform
reasons for cracking
- it helps to match the supply of fractions with the demand for them
- it produces alkenes, which are useful as feedstock for the petrochemical industry
supply and demand of hydrocarbons
-the supply is how much of a fraction an oil refinery produces
-the demand is how much of a fraction customers want to buy
how cracking fixes issues with supply & demand
-fractional distillation of crude oil often produces more of the larger hydrocarbons than can be sold, and less of the smaller hydrocarbons than customers want
-smaller hydrocarbons are more useful as fuels than larger hydrocarbons
-since cracking converts larger hydrocarbons into smaller hydrocarbons, the supply of fuels is improved
-this helps to match supply with demand
alkenes vs alkanes
-alkanes are saturated (their carbon atoms are only joined by C-C single bonds)
-alkenes are unsaturated (they contain at least one C=C double bond
-alkenes are more reactive than alkanes & can take part in reactions that alkanes cannot
saturated
no carbon-to-carbon double bonds, only single bonds
unsaturated
contains at least one double or triple bond
production of petrol
-non-renewable fossil fuel
-made from crude oil, finite
-some of the substances found in petrol are made by cracking crude oil fractions, a process which uses large amounts of energy
production of hydrogen
3 ways
1. reaction of methane with steam
2. cracking of crude oil fractions
3. electrolysis of water
combustion products of petrol vs hydrogen
petrol:
(incomplete combustion)
-carbon particles = smoke and soot
-carbon monoxide
hydrogen:
-water is the only product of combustion when hydrogen is used
hydrogen as fuel v petrol as fuel
(both very flammable)
energy released per kg of fuel (MJ):
142 (h)
46 (p)
state at room temperature and pressure:
gas (h)
liquid (p)
why is hydrogen usually liquefied by cooling or stored as a gas under pressure?
-hydrogen is a gas at room temp & pressure, its molecules are spread far apart so not very much can be stored in a given volume
if it is liquefied or pressurised, more can be stored
composition of modern atmosphere
-78% nitrogen
-21% oxygen
-0.9% argon
-0.04% CO2
compared to the earth’s early atmosphere, the modern atmosphere contains:
-less water vapour
-less carbon dioxide
-more oxygen
the earth’s early atmosphere probably contained…
-little or no oxygen
-a large amount of carbon dioxide & water vapour
-small amounts of other gases, such as ammonia and methane
how do we know there was little to no oxygen in the earth’s early atmosphere?
some ancient rocks contain iron compounds that break down in the presence of oxygen, they could only have formed if there was little or no oxygen at the time
how do we know there was a large amount of carbon dioxide & water vapour in the earth’s early atmosphere?
a volcano releases large volumes of carbon dioxide and water vapour, since the early atmosphere was produced by volcanic activity, it was likely to have contained a large amount of carbon dioxide and water vapour
why does the earth’s modern atmosphere have less water vapour than before?
-the earth cooled after it formed
-when it became cool enough, water vapour in the atmosphere condensed to liquid water & fell as rain, creating the oceans
why does the earth’s modern atmosphere have less carbon dioxide than before?
-carbon dioxide is a very soluble gas, it dissolves readily in water
-as the oceans formed, carbon dioxide dissolved and the amount in the atmosphere decreased
why does the earth’s modern atmosphere have more oxygen than before?
-plants make their own food by photosynthesis
-this forms glucose and oxygen from carbon dioxide and water
-photosynthesis by primitive plants and algae caused the removal of carbon dioxide from the air and the release of oxygen
how do greenhouse gases support the earth?
absorb heat radiated from the earth & release energy in all directions, which keeps the earth warm
examples of greenhouse gases:
carbon dioxide, water vapour, methane
the greenhouse effect
-infrared radiation from the sun is only partly absorbed by the earth
-the rest is radiated into the atmosphere
-although some of the infrared radiation escapes, some is absorbed by greenhouse gases
-this keeps the energy in the atmosphere, warming it up
global warming
gradual warming of the atmosphere over many years
how are humans increasing the amounts of greenhouse gases in the atmosphere?
-carbon dioxide formed by burning fossil fuels
-methane formed by cattle farming
climate
the average weather over a long time and over a large area
the effects of climate change:
-glaciers and polar ice melting
-sea levels rising
-rainfall changing, producing floods or droughts
-habitats changing
ways to mitigate the effects of climate change:
-building flood defences to manage floods from rivers and seas
-building irrigation systems to provide water in droughts
-planting different crops, better adapted to a new climate
(these steps are expensive, need to be on a large scale, and may themselves harm the environment)
