Chemistry 163B W2014 Lectures Electrochemistry Quickie

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Deborah Woods
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1 Chemistry 163B W014 Lectures 4-5- Electrochemistry Quickie ctivity coefficients for ions (W9 #58) Chemistry 163B Electrochemistry B s B q q ( ) ( ) ( ) K B sp ( s) B ( q) ( q) B ( s) 1 B B ( q) ( q) B cnnot B but only determine nd independently B 1 K sp 3 B 1M 1M 1 (1) K 3 B sp work of expnsion hydrogen pressure [ concentrtion ] cell (rection I of III) (10 br) ö (1 br) pfft 1 br 1 br 10 br 10 br 3 (10 br) ö (1br) RT Q rection 0 is for rection ( 1 br) ( 1 br) 1 br) RT kj per mole ( 10 br) 4 d nd work-other (did before for dg) responsible for 3 redox rections; here s II (W9, prob #60) d d TdS SdT - - d d q TdS SdT Vd d wother 0 by nd lw d T, d- w other (very generl) e for spontneous process t constnt T, the MAXIMUM work done ON SURROUNDINGS is nd this occurs when the process pproches REVERSIBILITY oxidtion node reduction cthode 5 e + (g, 1 br) + Ag(s) ö + [1M] + - [1M] +Ag(s) + e 6 1

Chemistry 163B W014 Lectures 4-5- Electrochemistry Quickie for the rection (see Appendix A, Tble 4.1 for dt; dditionl deciml plces from other tbles) nd FINALLY w other!!! (p.

2 Chemistry 163B W014 Lectures 4-5- Electrochemistry Quickie for the rection (see Appendix A, Tble 4.1 for dt; dditionl deciml plces from other tbles) nd FINALLY w other!!! (p. 0) e + (g, 1tm) + Ag(s) ö + [1M] + - [1M] + Ag(s) +e f ºG f (kj) ºG = - (0) - ( ) + (0) + (-131.3) + (0) = kj =for moles e trnsferred e + ½ (g, 1tm) + Ag(s) ö + [1M] + - [1M] + Ag(s) + e ºG=-1.44 kj per ½ mole for 1 mole e trnsferred 7 8 w other (p. 60) p. 60 vs is overcomplicted dw - electricl dq BUT sign of F nd spontneity electric potentil dq Fdn chrge trnsfer moles of e s trnsferred w T, other irrev irrev T, cell cell T, cell cell for irreversible = mf for reversible from negtive chrge on e dw - w electricl electricl F is Frdy constnt 96,458 coulomb (mole e) 1 Fdn (n electrons trnsferred) w electromotive force= E& R p60 z -n rev T, < 0 spontneous F > 0 spontneous UNITS: [w] = [Q] [F] joule= coulomb volt 9 10 vs F responsible for 3 redox rections; here s II (W9, prob #60) RT Q rection RT Q rection RT Q T 98K rection V Q n rection n = moles electrons trnsferred n =mol 1 n= n mol n unitless 11 oxidtion node reduction cthode F V e + (g, 1br) + Ag(s) ö + [1M] + - [1M] +Ag(s) + e 0.33 V 1

3 Chemistry 163B W014 Lectures 4-5- Electrochemistry Quickie exmple incorporting ctivities exmple incorporting ctivities e + (g, 1br ) + Ag(s) ö + [1M] + - [1M] + Ag(s) +e V Ag ( s ) n Ag( s) Ag Ag 1 [ ] [ ] cn't independently mensure nd V [ ] [ ] n V [ ] [ ] n 0.33 V e s V [1 M] [1 M] 0.33 V (1 br) unitless; hve dropped stndrd stte concs nd pressure from denomintors exmple incorporting ctivities intensive F vs extensive F = - ( /) V [1 M] [1 M] 0.33 (1 br) (g, 1 br) ö + [1M] +e e + Ag(s) ö - [1M] + Ag(s) F= 0 V F= 0.33 V culte s from observed F (W9, prob 60) If s = V 0.33 V V 1 mol 96,485 C mol 0.33V CV 4.90 kj e + (g, 1 br) + Ag(s) ö + [1M] + - [1M] + Ag(s) +e F cell = 0.33 V = kj for moles e trnsferred V ( ) ' Ag s cell e scell Ag( s) = kj for moles e trnsferred [from f erlier ] intensive F vs extensive F = - ( /) intensive F vs extensive F = - ( /) ½ (g, 1 br) ö + [1M] +e F= 0 V = kj for moles e trnsferred e + Ag(s) ö - [1M] + Ag(s) e +½ (g, 1 br) + Ag(s) ö + [1M] + - [1M] + Ag(s) +e F cell= 0.33 V = kj for 1 moles e trnsferred V ( ) 1 Al s cell e cell Ag ( s) F= 0.33 V F intensive sme s for mole e s F is oomph per electron 17 e 1e two times greter extensive: depends on stoichiometry V Ag ( s ) Ag( s) cell e' s cell = kj for 1 moles e trnsferred V ( ) 1 Ag s cell e cell Ag ( s) cell e cell 1e sme F intensive: independent of how rection is written ooomph ER electron 18 3

4 Chemistry 163B W014 Lectures 4-5- Electrochemistry Quickie biologicl exmple: cytochrome C iron contining enzyme (rection III) biologicl exmple (redox eqution III) oxidtion reduction CytC=cytochrome C stndrd stte p=7, [+]=10 7 stndrd REDUCTION potentils e + CytC(Fe 3+ ) ö CytC(Fe + ) e + ½O (g) + + (q) ö O ({) rection: the oxidtion of CytC(Fe + ) CytC(Fe + ) ö CytC(Fe 3+ ) + e e + ½O (g) + + (q) ö O ({) ½O (g) + + (q) +CytC(Fe + ) ö CytC(Fe 3+ ) + O ({) F red (V) p F(V) ?= F cell ½O (g) + + (q) +CytC(Fe + ) ö CytC(Fe 3+ ) + O ({) RT RT ' ' cell cell Q cell 1 [ ] O O 7 wht s º? wht s Q? wht s n? 10 M 1br stndrd stte stndrd stte [ + ]= F nd thermodynmic derivtives, etc. (W9, prob #59) ΔC p from Φ RT K RT K eq S S T T T T T T T T eq 1 S S T T TS TS T T Cp T T T T T T Cp T reltionships on finl btteries nd fuel cells Electrochemistry: rection = cell RT Q V Q tt 98K n bttery - nicely pckge electrochemicl cell closed system runs irreversibly (F < û) my be rechrged (storge bttery) fuel cell- electrochemicl cell open system (rectnts continuously flow in) 3 4 4

Chemistry 163B W014 Lectures 4-5- Electrochemistry Quickie efficiency of w electricl vs w -V types of btteries compre: w electricl (on surr) from led storge bttery DG=-377 kj mol -1, D =-8 kj mol -1

5)*8 kj mol -1 = 114 kj mol -1 bttery: DG=-377 kj mol -1, T=300K w electricl =- DG = 377 kj mol -1 Alkline storge (no liquids) Zn(s) oxidized to Zn + MnO reduced to Mn O 3 the winner: welectricl 377

5 V 6 types of btteries Li-ion btteries NiM- Nickel Metl ydride M= intermetllic compound, e.g.

into smller nd lighter weight units thn other types of btteries. Those ttributes hve spurred enormous growth in their use for cell phones, lptop computers, nd other portble electronic devices.

slts in orgnic solvents such s ethylene crbonte nd ethyl methyl crbonte. This is not the cse for other commercil bttery types. 8 bttery property comprison Zinc 1.

owever, reductions in the price of Alklines hve mde both Zinc-Crbon nd Zinc-Chloride btteries ll but obsolete. Alkline 1.

5 Chemistry 163B W014 Lectures 4-5- Electrochemistry Quickie efficiency of w electricl vs w -V types of btteries compre: w electricl (on surr) from led storge bttery DG=-377 kj mol -1, D =-8 kj mol -1 with w -V (on surr) of het engine using q upper =-D storge bttery Led storge b(s) oxidized to b + bo reduced to b + het engine: T u =600K, T L =300K e=( )/600= 0.5 w -V =(0.5)*8 kj mol -1 = 114 kj mol -1 bttery: DG=-377 kj mol -1, T=300K w electricl =- DG = 377 kj mol -1 Alkline storge (no liquids) Zn(s) oxidized to Zn + MnO reduced to Mn O 3 the winner: welectricl w V Zn (s) + O - (q) ZnO (s) + O (l) + e +1.6V MnO (s) + O (l) + e Mn O 3 (s) + O (q) 0.75 Zn (s) + MnO (s) ZnO (s) + Mn O 3 (s) +1.5 V 6 types of btteries Li-ion btteries NiM- Nickel Metl ydride M= intermetllic compound, e.g. M=AB 5, A is rre erth mixture of thnum, cerium, neodymium, prseodymium B is nickel, coblt, mngnese, nd/or luminum Ni + oxidized to Ni 3+ + reduced to -, M oxidized Li-ion btteries cn pck more energy into smller nd lighter weight units thn other types of btteries. Those ttributes hve spurred enormous growth in their use for cell phones, lptop computers, nd other portble electronic devices. O + M + e - ØO - + M Ni(O) + O - ØNiO(O) + O + e - igh power Ni-M bttery of Toyot NW0 rius 7 A downside of Li-ion cells, however, is tht they contin flmmble electrolyte solution consisting of lithium slts in orgnic solvents such s ethylene crbonte nd ethyl methyl crbonte. This is not the cse for other commercil bttery types. 8 bttery property comprison Zinc 1.5V Non-rechrgeble first the forerunner nd lter n inexpensive lterntive to Alkline btteries. owever, reductions in the price of Alklines hve mde both Zinc-Crbon nd Zinc-Chloride btteries ll but obsolete. Alkline 1.5V Rechrgeble Alkline rechrgeble btteries re lower cpcity (don t hold chrge s long) thn the more populr NiM rechrgebles. The dvntge of the rechrgeble Alkline over the NiM or the NiCAD is tht it loses its chrge grdully, Nickel-Metl ydride (NiM) 1.5V Rechrgeble- Lightweight nd rechrgeble, the NiM hs higher cpcity thn the NiCAD plus you cn throw it wy since it doesn t contin toxic metls nd it isn t clssed s hzrdous wste item. Lithium ion 3.6V Rechrgeble For given voltge, lithium ion bttery is smller in size nd lighter in weight thn nickel cdmium (NiCd) or nickel metl hydride (NiM) bttery. In ddition, lithium ion hs virtully no self-dischrge. This llows lithium ion bttery to be stored for months without losing chrge. The bttery chemistries cn be compred s follows: 9 fuel cells EM- proton exchnge membrne lod O Ø + + e - 0 V ½O e - Ø O 1.3 V Fuel cells come in vriety of sizes. Individul fuel cells produce reltively smll electricl potentils, bout 0.7 volts, The energy efficiency of fuel cell is generlly between 40 60%. 30 5

6 Chemistry 163B W014 Lectures 4-5- Electrochemistry Quickie i the electrochemicl potentil dg dw SdT Vd i dni elec i, G rection w T, elec i i = rection 0 i, End of Lecture dg SdT Vd i dni i, VS Grectio n 0 T, i i i, 31 ( ) i i dw i elec i ssigns electricl work to ech species including electrons trnsferred 3 6

Chemistry 163B. Electrochemistry

Chemistry 163B. Electrochemistry Chemistry 163B Electrochemistry 1 activity coefficients for ions (HW9 #58) BaCl s Ba aq Cl aq a a ( ) ( ) ( ) K sp BaCl ( s) 1 a ( ) a Ba aq Cl ( aq) Ba Ba ( aq) Ba a Cl ( aq) Cl a Cl BaCl ( s) cannot