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3/4 CHEMISTRY > U3AOS1: fuels & energy from fuels > Flashcards

U3AOS1: fuels & energy from fuels Flashcards

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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
Q

vaporisation _______ as temp increases

A

increases, so flammable and combustible liquids are more hazardous at temps higher than room temp. vapours react w air and burn, not liquid itself

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26
Q

what happens in a transesterification reaction

A

triglyceride + 3 methanol -> fatty acid methyl esters + glycerol (KOH CATALYST)

this is a true transesterification reaction bc changes ester -> ester

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27
Q

only ESTERIFICATION equation from just fatty acids

A

fatty acid + methanol -> fatty acid methyl ester + water

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28
Q

advantages of biodiesel

A

-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)

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29
Q

disadvantages of hygroscopicity in biodiesel

A

decrease heat of comb, increase amount of smoke, increase corrosion of fuel system, water freezes so ice may be present in fuel lines

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30
Q

disadvantages of biodiesel

A

-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

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31
Q

at a temp of 10 deg, is biodiesel better (cloudpoint of 15 deg) or petrodiesel (cloudpoint of 5 deg)?

A

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

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32
Q

define cloudpoint

A

the highest temperature at which wax forms and fuel looks cloudy -> crystals are formed

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33
Q

what is the word you link with biodiesel?

A

METHYL ESTERS

34
Q

which has a higher energy content - petrodiesel or biodiesel?

A

-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
Q

advantages of biogas

A

-renewable
-CO2 absorbed during photosynthesis
-made from plant and organic waste
-reduces waste disposal
-low running costs

36
Q

disadvantages of biogas

A

-low energy content
-supply of waste raw materials limited

37
Q

advantages of bioethanol

A

-renewable
-CO2 absorbed during photosynthesis
-burns smoothly
-fewer particulates produced compared to petrol

38
Q

disadvantages of bioethanol

A

-lower energy content than petrol
-may require use of farmland otherwise used for food production

39
Q

advantages of coal

A

-large reserves
-relatively high energy content

40
Q

disadvantages of coal

A

-non renewable
-high level of emissions
-less easily transported

41
Q

advantages of natural gas

A

-more efficient than coal for electricity
-easy to transport through pipes
-relatively high energy content

42
Q

disadvantages of natural gas

A

-non renewable
-limited reserves
-polluting, contrib to greenhouse effect

43
Q

what bonds are there b/w biodiesel molecules

A

dispersion forces
dipole dipole forces
NOT hydrogen bonds

44
Q

q=_______

A

q=mcAT

45
Q

Q=_______

A

Q=n x enthalpy change/coefficient

46
Q

biodiesel has ______ compared to petrodiesel in terms of combustion products

A

-decreased CO production
-increased emission of particulate matter
-increased emission of nitrogen oxides

47
Q

why does propan-1-ol have a higher bp than propane?

A

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
Q

give three examples of biofuels

A

biogas
bioethanol
biodiesel

49
Q

give examples of fossil fuels

A

coal
crude oil
petroleum gas
coal seam gas

50
Q

does biodiesel have higher hygroscopicity or petrodiesel?

A

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
Q

which has a higher viscosity: biodiesel or petrodiesel?

A

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
Q

define hygrscopicity

A

the ability to absorb water

53
Q

would melting point be higher in a biodiesel produced by saturated or unsaturated fatty acids?

A

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
Q

how to find energy released per gram of fuel from heat of combustion (molar)

A

divide molar energy release / molar mass of compound

55
Q

define hess’ law

A

law = allows the overall enthalpy change for a reaction to be calculated from sum of the enthalpies of indiv reactions comprising it

56
Q

define activation energy

A

the minimum energy required to break bonds between reactants and initiate the chemical reaction
can be reduced via catalysts

57
Q

state change in exo reaction

A

gas -> liquid -> solid (releasing energy)

58
Q

state changes in endo reaction

A

solid -> liquid -> gas (absorbing energy)

59
Q

in q=n x ^H reaction, why is it delta H and not heat of c?

A

-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
Q

mass=______

A

density x volume

61
Q

why is the experimental heat of c likely to be lower than theoretical heat of c?

A

-incomplete combustion
-incomplete oxidation
-heat loss to environment
-not at SLC

62
Q

why may validity still be higher when there was a different mass of water and fuel used?

A

-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
Q

in heat of combustion experiments, why is a metal can used and not a heat proof beaker?

A

allows better heat transfer SO more accurate results w. the enthalpy change calculations

64
Q

in heat of c experiments, how do you improve the accuracy of the calculated value of heat of c?

A

-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
Q

are dipole dipole forces or bonds?

A

NOT BONDS
interactions/forces

66
Q

define transesterification

A

involves a chemical reaction where one type of ester is turned into another

67
Q

write the word equation and balanced formula equation for the fermentation of ethanol

A

Glucose —–(bacteria)—-> Ethanol + Carbon dioxide

C6H12O6 (aq) ——(bacteria)—->2CH3CH2OH(l) + 2CO2(g)

(note the glucose in the fermentation equation is aq. aqueous

68
Q

when is a hydrocarbon a liquid?

A

when it is longer than pentane

69
Q

what is the state symbol for glucose in fermentation?

A

aqueous

70
Q

what is the state symbol for ethanol in fermentation?

A

aqueous

71
Q

what is the state symbol for water in combustion reactions?

A

liquid - can be gas if higher that 100 deg celsius or reaction is happening in a fuel cell

72
Q

what is the state symbol for ethanol as a fuel?

A

liquid

73
Q

how to improve reliability of results?

A

repeat
take avg of results to minimise impact of random errors
increase precision + reliability

74
Q

what does a H bond look like?

A

NOF-H - - - - - - - - - - - NOF
forms between POLAR regions of molecules

75
Q

what does energy density refer to?

A

relates to the energy released per gram of the fuel, NOT molar heat of combustion

76
Q

dispersion forces are formed through…

A

formed through non-polar regions of molecules. general electrostatic force of attraction b/w all molecules bc of moving electrons

77
Q

dipole dipole forces occur through…

A

POLAR REGIONS OF MOLECULES

78
Q

is wood a fuel?

A

yes, has a very low energy content

79
Q

what molecules are contained in petrodiesel?

A

hydrocarbons that are longer that C8 - long chain hydrocarbons

80
Q

what is the state symbol for fuels?

A

liquid. not aqueous bc we do not burn fuels containing water in them - inefficient and release net lower energy

81
Q

do products or reactants have stronger bonds in an exothermic reaction?

A

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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