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
what is the word you link with biodiesel?
METHYL ESTERS
which has a higher energy content - petrodiesel or biodiesel?
-petrodiesel b/c its a long straight chain of hydrocarbons that is combusted to release max amount of energy
-biodiesel is already partially oxidised bc of oxygen present, SO they don’t contribute to energy release + combustion of energy
advantages of biogas
-renewable
-CO2 absorbed during photosynthesis
-made from plant and organic waste
-reduces waste disposal
-low running costs
disadvantages of biogas
-low energy content
-supply of waste raw materials limited
advantages of bioethanol
-renewable
-CO2 absorbed during photosynthesis
-burns smoothly
-fewer particulates produced compared to petrol
disadvantages of bioethanol
-lower energy content than petrol
-may require use of farmland otherwise used for food production
advantages of coal
-large reserves
-relatively high energy content
disadvantages of coal
-non renewable
-high level of emissions
-less easily transported
advantages of natural gas
-more efficient than coal for electricity
-easy to transport through pipes
-relatively high energy content
disadvantages of natural gas
-non renewable
-limited reserves
-polluting, contrib to greenhouse effect
what bonds are there b/w biodiesel molecules
dispersion forces
dipole dipole forces
NOT hydrogen bonds
q=_______
q=mcAT
Q=_______
Q=n x enthalpy change/coefficient
biodiesel has ______ compared to petrodiesel in terms of combustion products
-decreased CO production
-increased emission of particulate matter
-increased emission of nitrogen oxides
why does propan-1-ol have a higher bp than propane?
bc of hydroxyl group present in propan-1-ol, then there are dipole-dipole bonds present bw molecules AND STRONGER DISPERSION FORCES, w/as propane has only weaker dispersion forces present. so more energy required to break strong IMF in propan-1-ol
give three examples of biofuels
biogas
bioethanol
biodiesel
give examples of fossil fuels
coal
crude oil
petroleum gas
coal seam gas
does biodiesel have higher hygroscopicity or petrodiesel?
bc biodiesel has polar ester func group, then can form H bonds w water molecules so increased tendency to attract water W/AS petrodiesel is of shorter, non-polar hydrocarbon chains held by weaker disp forces and NO H BONDS so weaker tendency to attract water
which has a higher viscosity: biodiesel or petrodiesel?
bc biodiesel has polar ester func grp, can form stronger IMF dipole-dipole forces w/as petrodiesel (non polar hc chain) only held by weaker disp forces. biodiesel = also longer hc chain so stronger dispersion forces. molecules packed more closely together so greater resistance to flow and more viscous`
define hygrscopicity
the ability to absorb water
would melting point be higher in a biodiesel produced by saturated or unsaturated fatty acids?
bc saturated fatty acids contain no C=C bonds, then molecules of the fatty acid can sit closely together and pack closely, so dispersion forces are stronger. w/as unsaturated fatty acids, w the presence of C=C bonds, results in a kink in the chains of the fatty acid. so, this reduces how effectively the mol can pack together and decreases disp forces. t/f, more energy required to break stronger IMF in satu fatty acids than other
how to find energy released per gram of fuel from heat of combustion (molar)
divide molar energy release / molar mass of compound
define hess’ law
law = allows the overall enthalpy change for a reaction to be calculated from sum of the enthalpies of indiv reactions comprising it
define activation energy
the minimum energy required to break bonds between reactants and initiate the chemical reaction
can be reduced via catalysts
state change in exo reaction
gas -> liquid -> solid (releasing energy)
state changes in endo reaction
solid -> liquid -> gas (absorbing energy)
in q=n x ^H reaction, why is it delta H and not heat of c?
-heat of c is always positive and not dependent on equation, so X take into account coefficients
-enthalpy change can be pos or neg and IS dependant on equation ie. coefficient in equation
-limitation in data book is only SLC
-delta h = per mol of reaction w/as heat of c = per mol of fuel
mass=______
density x volume
why is the experimental heat of c likely to be lower than theoretical heat of c?
-incomplete combustion
-incomplete oxidation
-heat loss to environment
-not at SLC
why may validity still be higher when there was a different mass of water and fuel used?
-provided the experiment is completed under same conditions, different masses of water and fuel not affect calculation
-enthalphy has not changed as a result bc the calculation takes into account different masses -> will be proportional to what is used
in heat of combustion experiments, why is a metal can used and not a heat proof beaker?
allows better heat transfer SO more accurate results w. the enthalpy change calculations
in heat of c experiments, how do you improve the accuracy of the calculated value of heat of c?
-place flame as close to metal can
-place a lid on the metal can to minimise heat loss
-insulate can with aluminium, steel to decrease heat loss
are dipole dipole forces or bonds?
NOT BONDS
interactions/forces
define transesterification
involves a chemical reaction where one type of ester is turned into another
write the word equation and balanced formula equation for the fermentation of ethanol
Glucose —–(bacteria)—-> Ethanol + Carbon dioxide
C6H12O6 (aq) ——(bacteria)—->2CH3CH2OH(l) + 2CO2(g)
(note the glucose in the fermentation equation is aq. aqueous
when is a hydrocarbon a liquid?
when it is longer than pentane
what is the state symbol for glucose in fermentation?
aqueous
what is the state symbol for ethanol in fermentation?
aqueous
what is the state symbol for water in combustion reactions?
liquid - can be gas if higher that 100 deg celsius or reaction is happening in a fuel cell
what is the state symbol for ethanol as a fuel?
liquid
how to improve reliability of results?
repeat
take avg of results to minimise impact of random errors
increase precision + reliability
what does a H bond look like?
NOF-H - - - - - - - - - - - NOF
forms between POLAR regions of molecules
what does energy density refer to?
relates to the energy released per gram of the fuel, NOT molar heat of combustion
dispersion forces are formed through…
formed through non-polar regions of molecules. general electrostatic force of attraction b/w all molecules bc of moving electrons
dipole dipole forces occur through…
POLAR REGIONS OF MOLECULES
is wood a fuel?
yes, has a very low energy content
what molecules are contained in petrodiesel?
hydrocarbons that are longer that C8 - long chain hydrocarbons
what is the state symbol for fuels?
liquid. not aqueous bc we do not burn fuels containing water in them - inefficient and release net lower energy
do products or reactants have stronger bonds in an exothermic reaction?
products
they are at a lower energy level, t/f more stable
have stronger bonds than reactants + energy is released as heat energy
