c.1 Energy SourcesWhat makes a good energy source?

1) Large amount of potential energy2) Released at reasonable rate to a useful form 3) With minimal pollution

Examples: efficiency of burning coal averages 30% (% thermal energy available from burning that becomes electricity)

- coal 7% less cost than gas for electricity- coal 19% less than nuclear sources for electricity

The more the quality of energy is degraded , the less efficient the fuel is:

Efficiency of energy transfer = useful output energy x 100% Total input energy

Worked example page 655

Energy Density – is a useful measure of the quality of a fuel, Specific energy – energy per unit mass

Energy density = energy released from fuel Specific energy = energy released from fuel Volume of fuel consumed Mass of fuel consumed

i.e 1 kg coal, natural gas, uranium-235 => 100W light bulb 4 days, 6 days, 140 years

Worked example page 656

Renewable energy resources- solar, wind, biomass, water, geothermal, fuel cells- geothermal widely used only 23% efficiency

c.2 Fossil Fuels

- storing energy (photosynthes) enabled the emergence of large organisms and the C-C bonds and the C-H bonds of our main energy supply.

- formation of fossil fuels of decaying organisms is reduction (i.e. methane)3 main

1) crude oil (petroleum) 2) gas 3) coal

Crude Oil - most important but difficult to use because mixture of hydrocarbon chain lengths (separated by boiling points (distillation) related to different vanderwaals forces into fractions of various chain lengths.

Longer chains, increased vanderwaals, higher temperature to make more gases, less volatile and less flammable

Shorter chains, decreased vanderwaals, lower temperature to make gases, more volatile and less flammable.

Cracking makes longer chain hydrocarbons into more useful shorter chain ones. (heating over a catalyst, zeolites)

Worked example pg 660 balanced equation for cracking

Octane Rating – a measure of the fuel’s ability to resist auto-ignition- higher octane fuels can be compressed more and give better performance than lower

octane ratings.- Octane rating increases with branching(i.e. 2,2,4 – trimethylpentane higher rating than

octane)- Octane rating decreases with increased length. Hexane higher rating than heptane- Aromatics rating is higher than that of straight chains with same number of carbons

Catalytic reforming – convert low-octane numbered alkanes into higher rating branched isomers(heating with platinum catalyst)

Oil refineries – use distillation, cracking, and reforming to produce valuable products.

Greener EnergyExamples of

- Scrubbing filters and engineered polymers which hold onto to sulfur compounds in fossil fuels (reduce SO2 emissions that cause acid rain)

- Produce lower environmental impact fuels, remove lead, benzene and sulfur from petrol; use of catalytic converter (reduce NOx, CO, SO2, lead oxides and carcinogenic benzene)

- Produce blended petroleum fuels, Mix ethanol with petrol, engines that run on liquefied petroleum gas or methane (reduce CO2 emissions, CO, NOx)

- Develop renewable and alternative resources, bioethanol, biodiesel, electric cars, hybrids, fuel cells (reduce dependence on oil, carbon neutral fuels which absorb CO2 as they grow.

Coal – is a more abundant fossil fuel than crude oil- Coal gasification – coal reacting with oxygen and steam to create hydrocarbons (synthesis

gas)- Process can occur underground, low plant costs, CO2 stored underground rather than into

atmosphere (carbon capture and storage, CCS)- Pollutants are washed out of the synthesis gas leaving a relatively clean efficient fuel- Also produces slag used in roofing or road construction, methanol, fertilizers

Coal Gasification

3 steps of Gasification

1) Pyrolysis: Coal CH4 + H2O or C + H2 or CO + CO2 or hydrocarbons Conditions: Some oxygen, temperature that will not allow combustion Process: Coal is dried into several gases and char

2)Reduction: C + H2O CO + H2 , C + CO2 2CO , CO + 3H2 CH4 + H2O ,CO + H2O CO2 + H2

Conditions: increase temperature, decrease oxygen, steam Process: synthesis gas (mainly CO + H2 is produced which can be burnt to produce electricity.

3)Clean-up: C + O2 CO2

Conditions: cooling chamber to remove synthesis gas, char burned off and impurities removed Process: Synthesis gas purified and removed, other useful material can be produced.

Coal liquefaction – takes cleaned synthesis gas and adds water or carbon dioxide over a catalyst (indirect coal liquefaction (ICL).

- Direct coal liquefaction (DCL) hydrogen is added to heated coal- Both methods adjust the carbon to hydrogen ratio to produce synthetic liquid fuels

nCO + (2n + 1)H2 CnH(2n+2) + H2O

Carbon Footprint – of a reaction is a measure of the net quantity of carbon dioxide produced by the process. i.e. biofuels may cost more to produce, but absorb CO2 in photosynthesis.

Worked example pg 664

C.3 Nuclear fusion and fission

Hydrogen Fusion – source of sun’s energy- Much more energy released than the fission on U-235 or Pu-239 (nuclear reactors)- Fusion of hydrogen nuclei to form helium releases heat and almost no nuclear waste, but

lots of energy to initiate, attractive prospect for energy generation.- Mass defect of a helium nucleus, weighs less than 2 protons and 2 neutrons.

Worked examples page 666 + 667

- E=mc2 - Electronvolts (eV) is a measure of the energy required to move one electron through a

predefined electric field. (1eV = 1.6022 x 10-19 J)- Helium nucleus has a lower potential energy than the sum of 4 unbound protons and

neutrons.- Mass defect has been converted to a binding energy (28 MeV) 7Mev/nucleon- Binding Energy: is the energy required to separate a nucleus into its constituent parts.

Nuclear processes: Fission and fusion

One of the proposed mechanisms for producing energy by controlled nuclear fusion here on earth.

- Deuterium and Tritium are fused into helium and a neutron is ejected. (mass defect occurs

converted into energy, tons of energy, difficult to contain)- Iron has the most stable nuclear configuration. - Fusing lighter elements to form larger ones the binding energy increases and the mass

defect is converted to energy.- The heavier transuranium elements can go through splitting or fission to form lighter nuclei,

as the sum of the binding energies of the 2 lighter elements is greater than the binding energy of a uranium-235

- Controlled nuclear fission is the process that powers nuclear generating plants currently

- In nuclear power plants some neutrons are absorbed by control rods in order to prevent a chain reaction from spiralling out of control. (# of rods and distance onto core can be controlled)

- Critical mass – material needed for the reaction to remain sustainable.- Critical - # of neutrons from one generation to the next remain constant- Supercritical - # of neutrons is increasing (meltdown possible)- Subcritical - # of neutrons is decreasing (not self-sustaining)

Types of Subatomic particlesAlpha particles – 2 p + 2 n (4

2He or α) (helium nucleus), largest particle, can travel few cm in air, limited hazardBeta particles – electron (0

-1e or β) , high speed, from nuclear decay, travel metres can cause burns to skinGamma ray – (ϒ) high frequency, short wavelength rays, high penetrating ability, can cause cancer, medicine for treatment, imaging and sterilization.Neutron – 1 atomic mass unit (1

0n) , can be released in fission and fusion rxns, high penetrating ability and can damage biological material Positron – antiparticle of an electron (0

+1 β+) , a positively charged beta particle, mass of electronProton – 1 atomic mass unit (1

1p or 11H) , positively charged.

Worked example pg 669

Half-life of a nuclear process- Some heavier elements are radioactive, spontaneous decay releasing alpha, beta and

gamma radiation, are first order reaction, constant half life.- -

-- Half life can be found by using the above graph or by calculations - No – starting material, N – remaining material, t – time interval

t½ = t ln2/ln(N0/N) or No = N x 2# of half lives

worked example pg 671

Radioactive Waste- The process of nuclear fission results in excess neutrons- Absorbed by control rods in nuclear reactor- Fission generates a large amount of dangerous radioactive waste which has to be disposed

of safely- Possibility of producing materials which could be used for nuclear weapons- Long half lives and harmful to living organisms- Long term storage of rods encased in steel surrounded by an inert gas and covered in

concrete

C.7 Nuclear fusion and nuclear fission (AHL)

Nuclear energyPg 703 worked example

Uranium Enrichment- Example above shows that converting 1 g of enriched U-235 to energy via fission releases

310 GJ which is equivalent to burning 140,000 kg of coal or about 93,000 L of gas and no CO2

- But it is only U-235 that can do this fission.- 99.28% isotope is U-238, so naturally occurring uranium must be enriched to increase the %

of U-235, involves separating U-235 isotope from U-238 isotope- Uranium mined as an ore with mixture of oxides, then processed to uranium (IV) oxide, UO2 - Convenient to separate isotopes in the gaseous state using diffusion as the lighter isotope

would diffuse more quickly (but UO2 ionic so melting and boiling points high)

Method 1- To achieve enrichment the following process is done:

UO2(s) + 4HF(g) UF4(s) + 2H2O(g)

UF4(s) + F2(g) UF6(g)

- UF6 – octahedral, non-polar, volatile (56°C). So U-235 easily separated from U-238- Solid UF6 is vaporized and forced through a membrane at high pressure, lighter isotopes

diffuse through faster (U-235) the gas with increased U-235 is collected and cooled- Needs to be repeated many times because increases concentration only a small amount.

Method 2- Centrifugation is used in this method not diffusion- Gaseous UF6 added to a centrifuge, U-238 drawn to the outside ad U-235 is extracted from

the centre

- Following enrichment by either method, UF6 gas reduced back to uranium metal then used as fuel.

Graham’s law of effusion - Rates of diffusion of the UF6 containing 2 isotopes can be calculated using this law - All UF6 at same temperature both isotopes have the same average kinetic energy

KE (235) = KE (238)

Example pg 706Radioactive decay- First order process

- Decay constant, (first order rate constant), is related to the half-life by: = ln 2/t1/2

- Level of radioactive decay decreases in proportion to the quantity of material remaining- Equation relating original quantity of material and the remaining quantity after time t has

passed:N = Noe-t No = original amount, N = remaining amount , t – time passed

Example pg 706

Risks associated with nuclear energy- Health risks ad storage problems, nuclear fuels may be used in weapons- Enrichment for generating electricity is 20%- Enrichment for nuclear weapons is 85% or more- One of the biggest dangers comes from ionizing radiation emitted by daughter products,

decay of nuclei and release of subatomic particles can damage living cells.- SI unit for radiation is the Sievert, Sv, measures effect on tissue I J/Kg- Annual background radiation is 2.4 mSv/year, 250 mSv detected in blood tests, 1 Sv

radiation poisoning signs such as nausea, headache and vomiting- In biological tissues ionizing radiation can remove electrons from molecules creating radicals

such as superoxide O2- and hydroxyl, HO· (these initiate chain rxns)

- O2- ion has strong oxidative properties, sometimes created naturally to kill foreign

microorganisms- HO· naturally from superoxide radical via Haber-Weiss rxn:

O2- + H2O2 O2 + HO·

Homework Pg 708 – 709 , Pg 673, Pg 664, Pg 657

C.4 Solar Energy

Photosynthesis – sunlight absorbed in cholorplasts by the chemical chlorophyll- Visible light can be absorbed by molecules that have a conjugated structure with an

extended system of alternating single and multiple bonds.- Visible light excites electrons and when they return to ground state they emit a photon of

light- In photosynthesis the return of the electron to ground state takes place during a complex

series of chemical reactions, net result is CO2 + H2O into glucose

- Pigments in plants are coloured due to conjugated double bond systems - i.e. if a certain pigment absorbs red and green or yellow, light as a result of its extended

conjugation, then blue or purple light will be reflected.- Violets are blue because anthocyanin pigment in the flower-

↔ Purpurin

Biofuels- Such as ethanol are obtained from corn sugar or glucose fermentation:

- Ethanol can be added to or blended with gasoline to conserve fossil fuels and ethanol is considered carbon neutral (CO2 in while growing , CO2 out when combusting)

- Biodiesel can be grown, used as a substitute for diesel (vegetable oils, highly viscous clogs up engine)

- Overcome viscosity problem by converting to less viscous esters with less intermolecular forces.

- i.e. transesterfication process is when a triglyceride is converted to esters and glycerol.

- other esterfications can produce shorter chain attachments to decrease intermolecular forces and decrease viscosity.

- mechanism of transesterfication (picture)

- in transesterfication to form biodiesel the vegetable oil is heated with NaOH catalyst and methanol to produce a methyl ester, or ethanol to produce the ethyl ester

- source for biodiesel varies depending on region i.e. fish fats (Alaska) , animal fats or vegetable oils

pg 677

advantages biodiesel disadvantage- high flash point - more viscous (pre-warming)- lower carbon footprint (grown) - slightly lower energy content

-agricultural land used, increases food prices- easily biodegradable, free of SO2 - more costly- sustainable - more nitrogen, more NOx

- a good solvent, clean engines - dirt cleaned from engines clogs filters

c.5 Environmental impact – global warmingHuman Influences and climate change- evidence exists that increased levels of greenhouse gases in the atmosphere produced by

human activities are changing the climate- raised levels of these gases are upsetting the balance of radiation entering and leaving the

atmosphere causing overall warming.

Natural greenhouse effect- high frequency radiation from sun is absorbed in upper atmosphere- UV, visible and longer wavelengths reach the surface where they are absorbed- Waves that are re-emitted from the surface are longer wave infrared (IR) and interacts with

the main GHGs methane, water vapour and carbon dioxide retaining heat (greenhouse)

-- The bonds of these molecules absorb the IR energy causing them to bend and stretch.- Frequencies of the IR and bending and stretching are similar- This causes increased vibration at certain frequencies- This can change the dipole moment, which can be detected by IR spectroscopy

- C-H , C=O and O-H bonds have resonance frequencies of vibration in the IR region.- % absorbance chart from textbook

Natural sources of greenhouse gases- Water vapour is of natural origin and accounts for 95% of all greenhouse gases - Absorbs IR radiation, as clouds reflects radiation away, self regulating- CO2 emissions since the industrial revolution have increased

2 grahs increase co2 and increase temperature

Greenhouse Gas emissions from Human Activities- Burning oil, natural gas and coal for energy production makes up 50% of anthropogenic GHG

emissions (CO2 from underground sources are entering the carbon cycle and increasing levels

- Factories add CO2, new NOx , 25% of anthropogenic, CFCs cholorfluorocarbons not naturally occurring

- Agriculture and deforestation account for 25% of anthropogenic, livestock flatulence, deforestation less photosynthesis

Carbon Sinks: The oceans- About 50% of the human CO2 emissions have been absorbed into sinks i.e. oceans 30%.- Ocean CO2 levels rising 1% per year since 1990- CO2 not very soluble, but once some dissolved: - CO2(aq) + H2O(l) ↔H2CO3(aq) ∆H = +- Increase in temp., lower CO2, therefore temp. lower near bottom increased CO2.- H2CO3(aq) + H2O(l) ↔ HCO3

- (aq) + H3O+

(aq)

- HCO3- (aq) + H2O(l) ↔ CO3

2- (aq) + H3O+

(aq)

Graph relating CO2 and ph

Measures to reduce greenhouse gas emissions

- Kyoto Protocol – international agreement to create carbon trading, to capture as much CO2 as they produced

Industry and Energy production – Carbon capture and storage (CCS) capturing waste CO2 from where it is produced and bringing it to storage sites so as not to enter atmosphere.- Scrubbers (coal power plants) remove SO2 and other GHGs

i.e. SO2(g) + H2O(l) + CaO(s) ↔ CaSO4*2H2O- Sequestration CO2 converted to a carbonate using silicate

i.e. MgSiO4(s) + 2CO2(g) 2MgCO3(s) + SiO2(s)

- combustion of fossil fuels frees up carbon stored underground, alternative synthesis gas- carbon recycling – use CO2 for synthesis fuels

Agriculture and deforestation- CH4 , methane , N2O , nitrous oxide main GHGs produced- Much smaller amounts than CO2, but CH4 x25 effect, N2O x300 effect- Sources enteric fermentation, anaerobic decomposition of organic matter, fertilizer use- Changing from nitrogen-based fertilizers to crop rotation methods could increase levels of

CCS- Use of urban space to grow crops could reduce CO2 and reduce transportation

Global dimming- Smoke, dust particles and clouds reflect sunlight back causes global dimming and cool’s the

earth.- Tiny particulates collect water and increase cloud cover in atmosphere- Polluted clouds reflect more light than non-polluted ones.- Estimates are that 2 - 3% less radiation reaches the earth’s surface due to polluted clouds

reflecting more.- So fossil fuel pollutants reduce as well as increase global warming- Global dimming pollutants cause acid rain, reduce evaporation of water and decrease

monsoon rains which causes lower crop yields in certain areas, local health problems from air pollutants

Effects of global warming on climate change- Melting permafrost- Less radiation reaching the earth’s surface- More devastating storms- Temp. becoming more extreme- Record levels rainfall and drought- Could put pressure on food and water resources

c.6 Electrochemistry, rechargeable batteries and fuel cellsBackground to battery technology

- Redox rxns electrons transferred from substance being oxidized to substance being reduced.- Spontaneous redox rxns are exothermic and the energy can be portable in the form of

batteries- Voltage depends on nature of material, low molar mass elements have a weight advantage- Luigi Galvani 1790 – first current between metals, Alessandro Volta 1810 first battery

Primary and secondary cells- Battery is a series of portable electrochemical cells- Primary electrochemical cell – materials consumed and not reversible, anode, electrolyte

are replaced or thrown away (cheaper)- Primary cells do not work well under high current demands such as electric cars, good for

low current, long storage devices i.e. smoke detectors, clocks, flashlights- Secondary cells – rechargeable batteries, reversible, stronger current demands, higher rate

of self discharge, charge before use.

Secondary cells: Lead-acid batteries- Rechargeables used in cars - Typical lead-acid battery in a car is recharged when driving and is used to create the ignition

spark- Can self discharge then you need to recharge it.- Electrolyte is H2SO4

Anode: Pb(s) + HSO4-(aq) PbSO4(s) + H+

(aq) + 2e-

Cathode: PbO2(s) + 3H+(aq) + HSO4

-(aq) + 2e- PbSO4(s) + 2H2O(l)

Cell Reaction: Pb(s) + PbO2(s) + 2H+(aq) + 2HSO4

-(aq) 2PbSO4(s) + 2H2O(l)

- During charging the above reaction is reversed and PbSO4 is the anode and cathode.

Secondary cells: Lithium-ion batteries

- Lithium atoms absorbed into a lattice of graphite electrodes for the anode.- Cathode is a lithium cobalt oxide complex, LiCoO2.- Lithium highest oxidation potential and small molar mass, great for batteries- Very high charge specific density compared to other rechargables- Electrolyte is non-aqueous, usually a gel polymer, because Li reacts with water

Cathode : Li+ + e- Li(s) (electrons accepted at graphite electrode)Anode: LiCoO2(s) Li+ + e- + CoO2(s)

- They hold charge better than the other rechargeables - Withstand many recharge cycles- They contain no heavy metals so considered safe for disposal- Disadvantages include sensitive to high temperatures, damaged if allowed to run flat, last

only a few years, can explode if overheated

Secondary cells: Nickel-cadmium batteries- Popular early choice but losing favour, low charge densities, lots of heavy metals- cathode NiO(OH) to Ni(OH)2 Ni3+ Ni2+

- anode cadmium metal to cadmium hydroxide Cd Cd2+

Anode: Cd(s) + 2OH-(aq) Cd(OH)2(s) + 2e-

Cathode: 2NiO(OH)(s) + 2H2O(l) + 2e- 2Ni(OH)2(s) + 2OH-(aq)

- low internal resistance allows for a quick recharge time- allow for full discharge without damage- disadvantages: high cost, heavy metals, lose charge quick at high temp.

Voltage of a cell- both types of cells, voltage is based off standard electrode potentials of the OA and RA.- Cells in series increases voltage (lead-acid car batteries 12 V)- Total # of electrons moving along with the energy given to them by the cell gives a measure

of the work that can be done by the current. This depends on the nature and surface area of the electrodes and charge density.

- Electrons in the external circuit provides us with useful energy, but each electrochemical cell has to move cations and anions inside the cell.

- Internal resistence depends on the ion mobility, electrolyte conductivity, electrode surface area

- Rxns occur faster at higher temp., at lower ones rxns are slower, ion mobility is reduced and battery internal resistence is reduced.

- Higher temp. , lower resistance, also higher rate of discharge, so store at lower temp.

- Electrodes with a large surface area allow for higher conductivity, high current needed to start a car

- Max current limited by internal resistance of the battery

Hydrogen Fuel Cells- Fuel cell is an electrochemical device that converts the chemical potential energy in a fuel

into electrical energy3 components

- 1) The proton exchange membrane (PEM) is the electrolyte and is a polymer which allows H+

ions to diffuse through but not electrons or molecules (acts as a salt bridge)- 2) The oxidizing and reducing electrodes which are catalysts that allow the chemical

reactions to occur.- 3) The bipolar plate which collects the current and builds up the voltage in the cell.

Anode: H2 2H+ + 2e-

Cathode: O2 + 4e- 2O2-

Cell Reaction: 2H2 + O2 2H2O

Alkali fuel cells - Alkali fuel cells were used to produce electricity and water- Electrolyte in these cells was a solution of potassium hydroxide (OH- source)- OH- migrate toward anode react with H+ producing water

alkali

- If electrolyte is acid H+ ions migrate toward cathode*In a PEM hydrogen cell (also acid electrolyte cell), water is formed at the cathode. In an alkali cell it is formed at the anode.*

Hydrogen Fuel sources- Hydrogen has to be very pure and needs platinum catalyst (expensive)- Hydrogen sources 1) electrolysis of water from wind or solar power - 2) reforming hydrocarbons or biofuels (I.e coal gasification or conversion of methane to

synthesis gas). Next hydrocarbons reacted with steam CxHy + xH2O xCO + H2

- 85% of hydrogen for fuel cells is made from method 2

Direct methanol fuel cell- Methanol provides H+ ions at the anode, fuel cell has the same components as the PEM cell

Anode: CH3OH + H2O 6H+ + 6e- + CO2

Cathode: O2 + 6H+ + 6e- 3H2OCell Reaction: CH3OH + O2 CO2 + 2H2O

- Energy density from direct methanol higher than hydrogen and lithium ion batteries- Produces CO2 not as clean as hydrogen fuel cells- Operates at 120°C versus H-cell 80°C- Needs more platinum catalyst

Comparing Fuels- Specific energy of hydrogen (energy to mass ratio) is more than double that of any other

fuel, so primary fuel choice, but also has a low energy density (energy to volume ratio) which requires more machinery and hence more mass to be added.

- Octane offers highest energy density but has environmental problems

Calculations for electrochemical cells

- Octane has a high energy density, fuel cells tend to have a higher thermodynamic efficiency- Thermodynamic efficiency is the ratio of the Gibbs energy change to the enthalpy change.

Thermodynamic efficiency = G/H

- G = -nFE and is a measure of the electrical energy output- H is the total chemical energy that would be released during combustion (some is lost to

heat as entropy in fuel cells)- Exa. Hc(H2) = -242 kJ G = -229kJ

Thermodynamic efficiency = -229kJ/-242 kJ = 95%- So fuel cells convert about 95% of the chemical energy to electrical

- Fuel cells may not operate at their maximum efficiency- For the previous kinds of question you may need to use section 12 and 13 of data booklet.

- Exa. Hydroge cell outputs 0.7 V- G = -nFE = -(2 x 96500 x 0.7) = -135100 J or -135.1 kJ

Thermodynamic efficiency = -135.1kJ/-242 kJ = 56%

Nernst Equation for a cell under non-standard conditions- Can change the EMF (voltage) of a cell by changing the concentration of the mobile ions- Standard cell 1 mol/L []’s ,100kPa pressure, 298K.- When these conditions are met voltage for a cell can be calculated using the half cell

potentials from section 24- Nernst Equation can be used for a non-standard cell

E = E- RT ln Q nF

E = EMF of standard cell R is the universal gas constant 8.31 JK-1mol-1

T is temp.in kelvin, 298K n is number of electrons from balanced equationF is Faraday constant 96,500 C mol-1

Q is reaction quotient, ratio of concentration ions undergoing oxidation to the concentration of ions undergoing reduction.

Q = [ions being oxidized] Q = [Zn 2+ (aq)] [ions being reduced] [Cu2+

(aq)]

For the cell: Cu2+(aq) + Zn(s) Zn2+

(aq) + Cu(s)

[Cu2+(aq)] = 1.5 mol dm-3, [Zn2+

(aq)] = 0.5 mol dm-3 E = E- RT ln Q = 1.10V – 8.31 x 298 x ln 0.5 = 1.10V –(-0.0141V) = 1.11V nF 2 x 96500 1.5

A concentration cell – has the same electrode in each half-cell, but the concentration of the ions in each half-cell is different

- Eventhough the metals are the same, a small potential difference is created

Microbial fuel cells- Converts chemical energy available from a substrate into electricity by anaerobic oxidation

carried out by microorganisms- Anaerobic oxidation of glucose produces H+ and electrons- Electrons collected at anode through wire go to cathode, while H+ ions diffuse through a

PEM, which forms water. - Bacteria that perform this live in the anode half-cell and can use acetate ion, carbohydrates

and waste water

Questions Pages 701, 686, 678

C.8 Photovoltaic cells and dye-sensitized solar cells - conjugated systems is the interactions of alternating double bonds to produce delocalized array of pi electrons - can absorbed visible light- all the carbons are sp2