U3AOS1: fuels & energy from fuels Flashcards
define fossil fuel
a natural fuel that is formed in the earth from fossilisation/decay of plant or animal matter from over millions of years ago
non renewable resource
energy conversions of coal
- chemical -> thermal
- thermal -> kinetic/mechanical
- kinetic -> electrical (usable)
comparing different forms of coal - 2 points
- amount of carbon + energy density
- amount of water, t/f vaporised in endothermic reaction
SO net energy release is less when more water is present bc cancel each other out
is producing electricity from coal an efficient process?
inefficient process
30-40% energy released only
b/c heat energy is lost to the environment in each of the steps
define coal + equation
a combustible fossil fuel formed by the partial decay of plant matter over mya
C (s) + O2 (g) –> CO2 (g)
how is crude oil sourced?
first drilled and extracted
separated via fractional distillation based on BP
cooler temp + gases rise to top, hotter temps + larger substance at bottom
substances tapped off
define petrodiesel
a liquid hydrocarbon fossil fuel obtained from crude oil (liquid bc long chain - anything after pentane is a liquid)
define coal seam gas
a natural gas sourced from coal deposits
define greenhouse effect
the process of warming the earth’s lower temp due to increased quantities of gases eg CO2
define non-renewable resouce
a resource that cannot be replenished at the same or faster rate than it is being consumed
define biofuel
a fuel sourced/derived from living or recently deceased plants and animals = BIOMASS
renewable resource
define biogas
a mixture of gases produced by the anaerobic breakdown of organic matter via bacteria eg. plant matter/biomass - contains 68% methane and 20% carbonv
define bioethanol
a fuel produced by the fermentation of glucose in organic matter by a microorganism called yeast
define biodiesel
a fuel produced by the esterification of fats and oils in organic matter eg. animal fats (saturated) and oil originating from crops, plant fats (unsaturated)
why may a biofuel not be completely carbon neutral?
while growth and consumption of biofuel = carbon neutral process, process of transportation and refining also released CO2
define carbon neutral
a fuel which does not result in a net production of carbon dioxide from sourcing or consumption
define renewable resource
a resource capable of being replenished by natural processes at a rate faster than or equal to consumption
define fuel
a substance with stored chemical energy that relatively easily releases usable amounts of energy eg as heat or power
safety dangers for fuels
low boiling point
low flashpoint
high flammability
easy to combust and release large amounts of energy
safety measures for fuels
keep away from naked flames
keep in well ventilated areas
use fuel specific fire extinguishers
use fire blankets
comparing two things formula
- structure
- intermolecular bonding
- properties
- uses + link to q
define flashpoint
the temp at which a particular organic compound gives off sufficient vapour to ignite in air -> not the boiling point
smaller hydrocarbons have weaker IMF and more easily vapourised so lower flashpoint
why do straight chain hydrocarbons have stronger IMF than branched chains?
straight chains sit and bond closely together eg. make rows of hydrocarbon t/f strong and slow IMF forces between chains W/AS branches on hydrocarbons push molecules apart so IMF acts over greater substance and weaker
define flammable liquid
any liquid with a flashpoint below 37.8 deg celsius, they ignite and burn easily at lowers temps
vaporisation _______ as temp increases
increases, so flammable and combustible liquids are more hazardous at temps higher than room temp. vapours react w air and burn, not liquid itself
what happens in a transesterification reaction
triglyceride + 3 methanol -> fatty acid methyl esters + glycerol (KOH CATALYST)
this is a true transesterification reaction bc changes ester -> ester
only ESTERIFICATION equation from just fatty acids
fatty acid + methanol -> fatty acid methyl ester + water
advantages of biodiesel
-CARBON NEUTRAL: lower net CO2 emissions when plant materials are grown = CO2 being absorbed in photosynthesis, partially offsets CO2 released in combustion
-NO SULPHUR so zero SO2 emissions when combusted -> X contribute to acid rain
-burns/combusts more completely bc of oxygen present in molecule (C=O bond makes it easier to oxidise)
disadvantages of hygroscopicity in biodiesel
decrease heat of comb, increase amount of smoke, increase corrosion of fuel system, water freezes so ice may be present in fuel lines
disadvantages of biodiesel
-lower energy content bc of ester link and strong dipole dipole forces -> bc of oxygen present, already partially oxidised and X contribute to energy release/combustion
-large amounts of land and water required
-hygroscopic (absorbs water) bc of ester link
-increased viscosity bc of polar ester grp - dipole dipole, so at even cooler temps, more viscous = X flow well
-higher cloudpoint than petro - so poor fuel flow at lower temp bc crystallises + forms gel
-more likely to oxidise - causing gum like substance to form in the fuel = block fuel lines and filters
at a temp of 10 deg, is biodiesel better (cloudpoint of 15 deg) or petrodiesel (cloudpoint of 5 deg)?
petrodiesel. bc cloudpoint is max/highest temp at which crystals form, then in petrodiesel, crystals will form below 5 deg celsius and the fuel will still be a liquid ie. no crystals formed at 10 deg. whereas, in biodiesel, crystals will have formed below 15 deg so will not be a good fuel
define cloudpoint
the highest temperature at which wax forms and fuel looks cloudy -> crystals are formed