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U3AOS1: fuels & energy from fuels Flashcards

1
Q

define fossil fuel

A

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

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2
Q

energy conversions of coal

A
  1. chemical -> thermal
  2. thermal -> kinetic/mechanical
  3. kinetic -> electrical (usable)
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3
Q

comparing different forms of coal - 2 points

A
  1. amount of carbon + energy density
  2. 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
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4
Q

is producing electricity from coal an efficient process?

A

inefficient process
30-40% energy released only
b/c heat energy is lost to the environment in each of the steps

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5
Q

define coal + equation

A

a combustible fossil fuel formed by the partial decay of plant matter over mya
C (s) + O2 (g) –> CO2 (g)

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6
Q

how is crude oil sourced?

A

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

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7
Q

define petrodiesel

A

a liquid hydrocarbon fossil fuel obtained from crude oil (liquid bc long chain - anything after pentane is a liquid)

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8
Q

define coal seam gas

A

a natural gas sourced from coal deposits

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9
Q

define greenhouse effect

A

the process of warming the earth’s lower temp due to increased quantities of gases eg CO2

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10
Q

define non-renewable resouce

A

a resource that cannot be replenished at the same or faster rate than it is being consumed

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11
Q

define biofuel

A

a fuel sourced/derived from living or recently deceased plants and animals = BIOMASS
renewable resource

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12
Q

define biogas

A

a mixture of gases produced by the anaerobic breakdown of organic matter via bacteria eg. plant matter/biomass - contains 68% methane and 20% carbonv

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13
Q

define bioethanol

A

a fuel produced by the fermentation of glucose in organic matter by a microorganism called yeast

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14
Q

define biodiesel

A

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)

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15
Q

why may a biofuel not be completely carbon neutral?

A

while growth and consumption of biofuel = carbon neutral process, process of transportation and refining also released CO2

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16
Q

define carbon neutral

A

a fuel which does not result in a net production of carbon dioxide from sourcing or consumption

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17
Q

define renewable resource

A

a resource capable of being replenished by natural processes at a rate faster than or equal to consumption

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18
Q

define fuel

A

a substance with stored chemical energy that relatively easily releases usable amounts of energy eg as heat or power

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19
Q

safety dangers for fuels

A

low boiling point
low flashpoint
high flammability
easy to combust and release large amounts of energy

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20
Q

safety measures for fuels

A

keep away from naked flames
keep in well ventilated areas
use fuel specific fire extinguishers
use fire blankets

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21
Q

comparing two things formula

A
  1. structure
  2. intermolecular bonding
  3. properties
  4. uses + link to q
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22
Q

define flashpoint

A

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

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23
Q

why do straight chain hydrocarbons have stronger IMF than branched chains?

A

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

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24
Q

define flammable liquid

A

any liquid with a flashpoint below 37.8 deg celsius, they ignite and burn easily at lowers temps

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25
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
26
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
27
only ESTERIFICATION equation from just fatty acids
fatty acid + methanol -> fatty acid methyl ester + water
28
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)
29
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
30
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
31
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
32
define cloudpoint
the highest temperature at which wax forms and fuel looks cloudy -> crystals are formed
33
what is the word you link with biodiesel?
METHYL ESTERS
34
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
35
advantages of biogas
-renewable -CO2 absorbed during photosynthesis -made from plant and organic waste -reduces waste disposal -low running costs
36
disadvantages of biogas
-low energy content -supply of waste raw materials limited
37
advantages of bioethanol
-renewable -CO2 absorbed during photosynthesis -burns smoothly -fewer particulates produced compared to petrol
38
disadvantages of bioethanol
-lower energy content than petrol -may require use of farmland otherwise used for food production
39
advantages of coal
-large reserves -relatively high energy content
40
disadvantages of coal
-non renewable -high level of emissions -less easily transported
41
advantages of natural gas
-more efficient than coal for electricity -easy to transport through pipes -relatively high energy content
42
disadvantages of natural gas
-non renewable -limited reserves -polluting, contrib to greenhouse effect
43
what bonds are there b/w biodiesel molecules
dispersion forces dipole dipole forces NOT hydrogen bonds
44
q=_______
q=mcAT
45
Q=_______
Q=n x enthalpy change/coefficient
46
biodiesel has ______ compared to petrodiesel in terms of combustion products
-decreased CO production -increased emission of particulate matter -increased emission of nitrogen oxides
47
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
48
give three examples of biofuels
biogas bioethanol biodiesel
49
give examples of fossil fuels
coal crude oil petroleum gas coal seam gas
50
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
51
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`
52
define hygrscopicity
the ability to absorb water
53
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
54
how to find energy released per gram of fuel from heat of combustion (molar)
divide molar energy release / molar mass of compound
55
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
56
define activation energy
the minimum energy required to break bonds between reactants and initiate the chemical reaction can be reduced via catalysts
57
state change in exo reaction
gas -> liquid -> solid (releasing energy)
58
state changes in endo reaction
solid -> liquid -> gas (absorbing energy)
59
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
60
mass=______
density x volume
61
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
62
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
63
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
64
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
65
are dipole dipole forces or bonds?
NOT BONDS interactions/forces
66
define transesterification
involves a chemical reaction where one type of ester is turned into another
67
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
68
when is a hydrocarbon a liquid?
when it is longer than pentane
69
what is the state symbol for glucose in fermentation?
aqueous
70
what is the state symbol for ethanol in fermentation?
aqueous
71
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
72
what is the state symbol for ethanol as a fuel?
liquid
73
how to improve reliability of results?
repeat take avg of results to minimise impact of random errors increase precision + reliability
74
what does a H bond look like?
NOF-H - - - - - - - - - - - NOF forms between POLAR regions of molecules
75
what does energy density refer to?
relates to the energy released per gram of the fuel, NOT molar heat of combustion
76
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
77
dipole dipole forces occur through...
POLAR REGIONS OF MOLECULES
78
is wood a fuel?
yes, has a very low energy content
79
what molecules are contained in petrodiesel?
hydrocarbons that are longer that C8 - long chain hydrocarbons
80
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
81
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

3/4 CHEMISTRY (8 decks)

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