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Prepared by Lawrence Kok
Option C Energy Density, Specific energy and CO2 global warming and ocean acidification.
Energy density = energy produced per unit vol
consumedvolumereleasedenergydensityEnergy... consumedmass
releasedenergyenergySpecific... %100
.
.
inputtotaloutputusefulEfficiency
Specific energy = energy produced per unit mass
Renewable ↓
Replenished at rate faster than it is used
Energy
Energy efficiency
Non renewable ↓
Used faster than they can be replaced
Renewable Non renewable
solar
hydro
geothermal
biomass
wind
nuclear
coal
gasoline
gas
Carbon footprint.
Strategies to reduce CO2 emission
Increase energy efficiency/conservation
Reduce dependency on carbon based Alternate source of energy (renewable)
Capture and storage from fossil fuel CO2 sequestration, reduce deforestration
Total amt greenhouse gas produced during human activity
Expressed in CO2 equivalent.
Find specific energy/energy density of hexane. (density hexane = 0.6548g cm -1)
∆H combustion hexane , ∆Hc = - 4163kJ mol-1
Formula C6H14 Mr = 86.2 g mol -1
86.2 g release - 4163 kJ 1 g release – 4163/86.2 = 48.3 kJ
36.1316548.02.86 cm
DensityMassVol
VolMassDensity
consumedmassreleasedenergyenergySpecific
...
consumedvolumereleasedenergydensityEnergy...
Energy density ↓
Specific Energy x Density
48.3 x 0.6548 = 31.6 kJcm-1
131.6 cm3 release - 4163 kJ 1 cm3 release – 4163/131.6 = 31.6 kJ cm-3
Power station generate power, 550 x 106 Js-1 . Overall efficiency of 36% for conversion of heat to electricity
Find energy generated (output) in 1 yearFind energy needed (input) for energy generation
Find mass coal used, assuming coal has ∆H of graphite
Total energy output550 x 106 x 60 x60x 24 x 365 = 1.73 x 1016J
1 year
kJinputTotal
inputtotal
inputtotaloutputusefulEfficiency
13
16
1082.4.
%100.1073.1%36
%100..
∆H comb graphite, ∆Hc = - 394kJ mol-1
M carbon Mr = 12 g mol -1
394 kJ released by – 1 mol C4.82 x 1013 kJ released by – 1.22 x 1011 mol C
1 mol C – 12 g1.22 x 1011 mol C – 1.47 x 1012 g of C
% mass carbon in coal – Highest CO2 emission highest when combusted
kJinputTotalinputtotal
inputtotaloutputusefulEfficiency
7
7
1071.4.
%100.1000.4%85
%100..
4.00 x 107 kJ energy required to heat a home. Methane combustion for heat is 85% efficient
∆H comb methane, ∆Hc = - 891 kJ mol-1
Formula CH4 Mr = 16 g mol -1
0.0221 x 106 cm3 release - 891 kJ 1 cm3 release – 891/0.0221 x 106
= 40126 kJ cm-3
Find mass methane required.
Find specific energy and energy density for CH4
∆H comb CH4 ∆Hc = - 891 kJ mol-1
Mr CH4 Mr = 16 g mol -1
(density CH4 = 723 x 10-6 g cm -
1) consumedmassreleasedenergyenergySpecific
... consumedvolume
releasedenergydensityEnergy...
16 g release - 891 kJ 1 g release – 891/16 = 55.5 kJ
Energy density ↓
Specific Energy x Density
55.5 x 723 x 10-6 = 40126 kJcm-1 36
6
100221.01072316
cmVol
DensityMassVol
VolMassDensity
Find % mass carbon in coal (CH), gasoline (C8H18), gas (CH4)Suggest why coal is a poor choice for fuel
% mass carbon in coal (CH)
%92%1001312
%100..
masstotalcarbonmass
% mass carbon gasoline (C8H18)
%84%10011496
%100..
masstotalcarbonmass
% mass carbon methane (CH4)
%75%1001612
%100..
masstotalcarbonmass
Coal burned to produce 500 x 103 kJ , has specific energy of 33 kJ g-1
Find mass coal burned, if efficiency is 38%.MF for coal is CH. Find mass CO2 produced
kJinputTotal
inputtotal
inputtotaloutputusefulEfficiency
6
3
1031.1.
%100.10500%38
%100..
33 kJ released by – 1 g coal1.31 x 106 kJ released by – 39900 g coal
↓Mol coal – 39 900/14 = 3062 mol
CH + 1.25O2 → CO2 + 0.5H2O 1 mol CH – 1 mol CO2
3062 mol CH – 3062 mol CO2
Mass CO2 – mol x RMMMass CO2 – 3062 x 44 = 135000g CO2
Fuel Specific energy/kJ g-
1
Carbon content by
mass/%
Coal 32 94Oil 42 83
hydrogen 142 0
Find CO2 produced for each 1000kJ energy from each sourceIdentify best and worse fuel used.
32 kJ released by – 1 g coal 1000 kJ released by – 31.3 g coal ↓% C by mass = 0.94 x 31.3 = 29.4 g C
C + O2 → CO2 1 mol C – 1 mol CO2
12 g C – 44g CO2
29.4 g C – (44 x 29.4)/12 = 108g CO2
42 kJ released by – 1 g oil 1000 kJ released by – 23.8 g oil↓% C by mass = 0.83 x 23.8 = 19.7 g C
C + O2 → CO2 1 mol C – 1 mol CO2
12 g C – 44g CO2
19.7 g C – (44 x 19.7)/12 = 72g CO2
142 kJ released by – 1 g H2
1000 kJ released by – 7 g H2
↓ % C by mass = 0
ZERO Emission CO2
Click here Carbon calculator
Energy density ↓
Specific Energy x Density
Fuel Formula ∆H combustion/kJ/mol-
1
Ethanol C2H5OH -1367
Coal C - 394
C2H5OH + 3O2 → 2CO2 + 3H2O 1 mol ethanol – 2 mol CO2
2.2 mol ethanol – 4.4 mol CO2
Which release more CO2 ?
Ethanol fuel
Mass CO2 – mol x RMMMass CO2 – 4.4 x 44 = 193g CO2
Coal fuel
C + O2 → CO2 1 mol C - 1 mol CO2
8.3 mol C – 8.3 mol CO2
Mass CO2 – mol x RMMMass CO2 – 8.3 x 44 = 366 g CO2
Find specific energy/energy density of ethanol and pure coal. (density ethanol/coal = 0.789 gcm -1 / 2267kg m-3)
Find carbon footprint in mass CO2 produced when 100g ethanol/coal burn
consumedmassreleasedenergyenergySpecific
...
46 g release - 1367 kJ 1 g release – 1367/46 = 29.7 kJ
Energy density ↓
Specific Energy x Density
29.7 x 0.789 = 23.4 kJcm-1
consumedmassreleasedenergyenergySpecific
...
12 g release - 394 kJ 1 g release – 394/12 = 32.8 kJ
32.8 x 2267 = 74.3 kJcm-1
Mass ethanol, 100g – 100/46 = 2.2 mol
Mass coal, 100g – 100/12 = 8.3 mol
1.33 x 106 kJ energy (output) required to heat a home. Find % mass carbon in two fuels
Find carbon footprint in terms of mass CO2 produced
Fuel Formula Specific energy/kJ
g-1
Efficiency /%
Coal CH 31 65Oil C5H9O4 22 70
% mass of carbon in Coal (CH)
%2.92%100112
12%.
..%.
carbon
masstotalcarbonmasscarbon
% mass of carbon in oil (C5H9O4)
%45%100)64()9()60(
125%.
..%.
carbon
masstotalcarbonmasscarbon
31 kJ released by – 1 g coal 2.05 x 106 kJ released by – 66000 g coal↓% C by mass = 0.922 x 66000 = 60 800g C
kJInput
inputtotal
inputoutputEfficiency
6
6
1005.2
%100.1033.1%65
%100
C + O2 → CO2 1 mol C – 1 mol CO2
12 g C – 44g CO2
60 800 g C – (44 x 60 800)/12 = 223000 g CO2
kJInput
inputtotal
inputoutputEfficiency
6
6
109.1
%100.1033.1%70
%100
22 kJ released by – 1 g oil 1.9 x 106 kJ released by – 86 400 g oil↓% C by mass = 0.45 x 86 400 = 38 900g C
C + O2 → CO2 1 mol C – 1 mol CO2
12 g C – 44g CO2
38 900 g C – (44 x 38 900)/12 = 142000 g CO2
Which release more CO2 ?
10 000 kJ energy (output) required to heat a home. Find carbon footprint in terms of mass CO2 produced
Fuel Formula ∆H combustion/kJ/mol-
1
Ethanol C2H5OH -1367
Methylbenzene C7H8 -3910
1367 kJ released by – 1 mol ethanol 10 000 kJ released by – 7.31 mol ethanol
C2H5OH + 3O2 → 2CO2 + 3H2O 1 mol ethanol – 2 mol CO2
7.31 mol ethanol – 14.6 mol CO2
Which release more CO2 ?
Ethanol fuel
Mass CO2 – mol x RMMMass CO2 – 14.6 x 44 = 643 g CO2
Methylbenzene fuel
3910 kJ released by – 1 mol C7H8
10 000 kJ released by – 2.56 mol C7H8
C7H8 + 9O2 → 7CO2 + 4H2O 1 mol C7H8 - 7 mol CO2
2.56 mol C7H8 – 17.9 mol CO2
Mass CO2 – mol x RMMMass CO2 – 17.9 x 44 = 789 g CO2
GHG allow short wavelength radiation to pass through but absorb longer wavelength, IR radiation from earth.
Some radiation is re radiated back to earth
Greenhouse Effect
Re radiated long wavelength Re radiated
long wavelength
Greenhouse Gases (GHG)
Gas Greenhouse
factor/GWP
Relative abundance/
%
Overall contributio
n
Carbon dioxide CO2 1 0.036 50
Water (H2O) 0.1 0.1 -
Methane(CH4) 30 0.0017 18
Dinitrogen oxide (N2O) 280 0.0003 6
Hydrofluorocarbon (HFC) 400-10000 - -
CFC 11000 - -
Perfluorocarbon (PFC) 9000 - -
Sulphur hexafluoride (SF6) 16000 - -
Global Warming Potential
Global Warming Potential (GWP)Compare ability of gas to absorb IR radiation to CO2 absorbing ability (as a std)
Water – main/abundant greenhouse gas – produced naturally – Contribution not significant
Molecule CO2 absorb IR • Vibration within molecule cause a net change in dipole moment • Freq of radiation matches vibrational natural freq of molecule radiation will be absorbed, causing a change in amplitude of molecular vibration.• Permanent dipole not necessary, only a change in dipole moment• Not all bond absorb IR . Bond must have an electric dipole (bond polarity) that changes as it vibrates.• Molecules absorb IR – cause changes in modes of vibration (stretch/bend)
IR Absorption and Molecular Vibration
Molecular Vibration
Stretching Mode Bending Mode
Symmetric Stretching• change in bond length
• bond become shorter/longer • IR ACTIVE (change in dipole)
• IR INACTIVE (No change in dipole)
Asymmetric Stretching• change in bond length
• bond become shorter/longer• IR ACTIVE (change in dipole)
• IR INACTIVE (No change in dipole)
Symmetric Bending• change in bond angle
• bond angle bigger/smaller• IR ACTIVE (change in dipole)
• IR INACTIVE (No change in dipole)
Asymmetric Bending• change in bond angle
• bond angle bigger/smaller• IR ACTIVE (change in dipole)
• IR INACTIVE (No change in dipole)
wagging twisting rocking scissoring
Greenhouse Effect
GHG allow short wavelength radiation to pass through but absorb IR longer wavelength radiation
Stretching Mode Bending Mode
Symmetric Stretching- Bond polarity cancel out
- NO change dipole moment- IR (inactive)
Asymmetric Stretching- change in bond length- change dipole moment
- Absorb IR (active)
Symmetric Bending- change in bond angle
- change dipole moment- Absorb IR (active)
Molecular Vibration for CO2
IR spectrum for CO2
Click here Spectra database (Ohio State) Click here Spectra database (NIST)
Molecular Vibration
Click here CO2 level (NASA)
Click here CO2 level (NOAA)
CO2 level over time
Click here CO2 level (CDIAC)
Click here CO2 level (NASA)
Click here CO2 level (NOAA)
CO2 level over time
Click here CO2 level (CDIAC)
Ocean acidification
Effect of ocean acidification-Decrease in pH level
- Disturb marine /coral reef development/ecosystem- CaCO3 needed for skeleton/shell for marine organisms
- Reduce ability of reef building coral to produce skeleton
Equilibrium bet CO2 (atmosphere) with aq CO2 (ocean)
Effect of increased CO2 level
Equilibrium bet CO2 (atmosphere) with aq CO2 (ocean) CO2 (g) ↔ CO2 (aq) ↓ CO2 (aq) + H2O ↔ H2CO3 (aq)
↓ H2CO3 (aq) ↔ H+ (aq) + HCO3
- (aq)
↓ HCO3
- (aq) ↔ H+ (aq) + CO3
2- (aq)
H+ ion (acidic)
Carbon Capture Storage/Sequestration (CCS)
i. Explain high solubility CO2ii. Predict sign ∆H sol for CO2 in water, deduce how its solubility increase with temp iii. High level CO2 lead to positive feedback whereby increase global temp are amplified. Exp its mechanism iv. Ocean acidification is due to a drop in pH from 8.2 to 8.1. Find the % increase in acidity.
Capture and storage from fossil fuel
i. CO2 – polar bond, form H2 bonding with water.
ii. ∆H solution –ve, due to strong H2 bonding with water (favourable)Increase in Temp- shift equi to left (endo) to reduce temp againHigh Temp – decrease CO2 solubility
iii. High Temp – amplify the process as less CO2 dissolve – more CO2 in atmosphere – higher temp
CO2 (aq) + H2O ↔ H2CO3 (aq)∆H = -ve polar bond polar
92.8
10
10
103.610][
][log2.8
][log
H
H
HpH
91.8
10
10
109.710][
][log1.8
][log
H
H
HpH%25%100
)103.6()109.7()103.6(%. 9
99
increase
H2 bonding
Acknowledgements
Thanks to source of pictures and video used in this presentation
Thanks to Creative Commons for excellent contribution on licenseshttp://creativecommons.org/licenses/http://spmchemistry.onlinetuition.com.my/2013/10/electrolytic-cell.htmlhttp://www.chemguide.co.uk/physical/redoxeqia/introduction.htmlhttp://educationia.tk/reduction-potential-tablehttp://2012books.lardbucket.org/books/principles-of-general-chemistry-v1.0/s23-electrochemistry.html
Prepared by Lawrence Kok
Check out more video tutorials from my site and hope you enjoy this tutorialhttp://lawrencekok.blogspot.com