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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