Chapter 7 Electrochemistry §76 Reversible cell Outside class reading vine: pp. 417 14.4 Galvanic cells pp. 423 14.5 types of reversible electrodes
Chapter 7 Electrochemistry §7.6 Reversible cell Levine: pp. 417 14.4 Galvanic cells: pp. 423 14.5 types of reversible electrodes Outside class reading
§76 Reversible cell 7.6.1 Basic concepts of electrochemical apparatus (1) Electrochemical apparatus Anode 078 Cathode Electrolytic cell; u Galvanic/voltaic cell Components Electrodes: positive/negative electrolytic solution? Reaction: oxidation reaction anode anodic reaction reductive reaction: cathode cathodic reactions
Electrolytic cell; Galvanic/voltaic cell (1) Electrochemical apparatus Reaction: oxidation reaction: anode, anodic reaction reductive reaction: cathode, cathodic reactions. Components: Electrodes: positive/negative electrolytic solution? 7.6.1 Basic concepts of electrochemical apparatus §7.6 Reversible cell
§76 Reversible cell 7.6.1 Basic concepts of electrochemical apparatus (2)Components of an electrode 1. Current collector(first-type conductor 2. Active materials: involves in electrochemical reaction 3. Electrolytic solution(second-type conductor) Question: Point out the current collector, active materials and electrolytic solution of the following electrode. 1)Zn(s) Zn*(sIn 2)(Pt), H2(g, Pe)H*(sIn
(2) Components of an electrode: 1. Current collector (first-type conductor) 2. Active materials: involves in electrochemical reaction 3. Electrolytic solution (second-type conductor). Question: Point out the current collector, active materials and electrolytic solution of the following electrode. 1) Zn(s)|Zn2+ (sln.) 2) (Pt), H2 (g, p)|H+ (sln.) 7.6.1 Basic concepts of electrochemical apparatus §7.6 Reversible cell
§76 Reversible cell 7.6.2 Interfacial reaction-half reaction and electrode reaction Differences between chemical and electrochemical reactions (e 2Fe3++ sn2 2Fe2++ Sn4+ at electrode/solution interface Interfacial reaction Fee sn: @irel half-reactions S Sn4++2 Fe3 2Fe3++2e-)2Fe in bulk solution cathode anode Principle for cell design: To harvest useful energy, the oxidizing and reducing agent has to be separated physically in two different compartments so as to make the electron passing through an external circuit
Differences between chemical and electrochemical reactions 2Fe3+ + Sn2+ ⎯→ 2Fe2+ + Sn4+ half-reactions: Sn2+ ⎯→ Sn4+ + 2e− 2Fe3+ + 2e- ⎯→ 2Fe2+ at electrode / solution interface in bulk solution Interfacial reaction 7.6.2 Interfacial reaction—half reaction and electrode reaction Principle for cell design: To harvest useful energy, the oxidizing and reducing agent has to be separated physically in two different compartments so as to make the electron passing through an external circuit. §7.6 Reversible cell
§76 Reversible cell 7.6.3 Reversibility of electrochemical cell (1)Relationship between chemical energy Thermodynamic reversibility and electric energy dG=-SdT+vdp+sw 1. Reversible reaction The electrode At constant temperature and pressure reaction reverts when shift from charge △G=W to discharge Reversible process: conversion of chemical reversible electrode energy to electric energy in a thermo dynamic reversible manner or vice versa. 2. Reversible pre △G=W"'=gv=-mFE 1→0, no current flows. Maximum useful work The relation bridges thermodynamics and electrochemistry
Maximum useful work (1) Relationship between chemical energy and electric energy At constant temperature and pressure Reversible process: conversion of chemical energy to electric energy in a thermodynamic reversible manner or vice versa. The relation bridges thermodynamics and electrochemistry §7.6 Reversible cell 7.6.3 Reversibility of electrochemical cell 1. Reversible reaction: The electrode reaction reverts when shift from charge to discharge. reversible electrode 2. Reversible process: I → 0, no current flows. Thermodynamic reversibility §7.6 Reversible cell d d d ' G S T V p W = − + + = G W ' = = − G W QV nFE ' =
§76 Reversible cell 7. 6. 4 Reversible electrodes ()basic characteristics 1)single electrode; Zn(Zn: Zn H 2)reversible reaction; Zn Z 2 3)the equilibrium can be easily attained and resumed. In order to acquire reversibility all reactants and products of the electrode reaction must be present at the electrode The stability of the electrode materials: According to the active series of metals, which kind of metal can form reversible electrode? K, Ca, Na, Mg, Al, Zn, Fe, Sn, Pb, (H), Cu, Hg, Ag, Pt, Au
7.6.4 Reversible electrodes (1) basic characteristics: §7.6 Reversible cell In order to acquire reversibility, all reactants and products of the electrode reaction must be present at the electrode. The stability of the electrode materials: According to the active series of metals, which kind of metal can form reversible electrode? K, Ca, Na, Mg, Al, Zn, Fe, Sn, Pb, (H), Cu, Hg, Ag, Pt, Au ?
§76 Reversible cell 7. 6. 4 Reversible electrodes The first-type electrode Cu(s) Cu2+(m) metal-metal ion electrode Cu A metal plate immersed in a solution Cult CurCuit +2e containing the corresponding metal ions Cu cu2+ C salt bridge Cu Fe electrode Cu electrode (1)Metal electrode Fe(NO3)2 Cu(NO3)2 (2)amalgam electrode solution solution (3)complex/coordination electrode
1) The first-type electrode: metal – metal ion electrode A metal plate immersed in a solution containing the corresponding metal ions. Cu (s) Cu2+ (m) (1) Metal electrode (2) amalgam electrode; (3) complex/coordination electrode; (4) gas electrode. 2 Cu Cu 2e + − + 7.6.4 Reversible electrodes §7.6 Reversible cell
§76 Reversible cell 7.6.4 Reversible electrodes 1)The first-type electrode: amalgam electrode Gas electrode Zn(Hg),Izn2+(m, Pt丝 Hydrogen electrode Zn2+2e+xHg、Zn(Hg H2 Pt(s)h,(g, pe)lH() complex electrode Three-phase electrode Ag(s)lAg(Cn)2(mu: g Ag(Cn),+e Ag+2CN P片H+ solution( liquid) Pt foil (solid) Basic characteristics 1) Two phases /One interface 2)Mass transport: metal cations only 10 mold H+ solution
Zn(Hg)xZn2+(m1 ): Ag(s)Ag(CN)2 (m1 ): amalgam electrode complex electrode Basic characteristics: 1) Two phases / One interface 2) Mass transport: metal cations only 1) The first-type electrode: Gas electrode: Three-phase electrode: H2 gas H+ solution (liquid) Pt foil (solid) Pt(s) H2 (g, p)H+ (c) Hydrogen electrode 1.0 mol·dm-3 H+ solution 7.6.4 Reversible electrodes §7.6 Reversible cell
§76 Reversible cell 7. 6. 4 Reversible electrodes Acidic hydrogen electrode hydrogen electrode Pt(s),H2(g, p)lH(c Pt(s), H2(g, p)loh(c) 2H(c)+2e→>H2(g,p) 2H2O(1)+2e→H2(g,p)+2OH(c) acidic B asic oxygen electrode oxvgen electrode Pt(s),o2(g, p)lh(c) Pt(s),o2(g, p)lOH(c) O2(g,p)+4H(c)+4e-→>2H2O()O2(g,p)+2H2O+4e-→>4OH(c)
Acidic hydrogen electrode Basic hydrogen electrode Pt(s), H2 (g, p)H+ (c) Pt(s), H2 (g, p) OH− (c) 2H+ (c) + 2e− → H2 (g, p) 2H2O(l) + 2e− → H2 (g, p)+2OH− (c) acidic oxygen electrode Basic oxygen electrode Pt(s), O2 (g, p)H+ (c) Pt(s), O2 (g, p)OH− (c) O2 (g, p) + 4H+ (c) + 4e− → 2 H2O(l) O2 (g, p)+ 2H2O + 4e− → 4OH− (c) 7.6.4 Reversible electrodes §7.6 Reversible cell
§76 Reversible cell 7. 6. 4 Reversible electrodes Important metal-insoluble salt-anion (2) The second-type electrode electrode metal-insoluble salt-anion electrode Hg( IHg, CL(s)ICr(c) A metal plate coated with insoluble salt containing the metal, and immersed in a Hg, Cl(s)+ 2e>2Hg ()+ 2Cl(c) solution containing the anions of the salt metal insoluble salt anion electrode There are three phases contacting with each other in the electrode AgCl Pb(s)pBsO (S)ISo. 2-(c): in lead-acid battery CI Ag(s) agCl(s) cl- Cl- Cl- PbSO4(S)+2e>Pb(s)+SO4(c) cr Cr AgCI(S)+e=Ag(s)+CI
(2) The second-type electrode: metal – insoluble salt-anion electrode A metal plate coated with insoluble salt containing the metal, and immersed in a solution containing the anions of the salt. metalinsoluble saltanion electrode Ag(s)AgCl(s)Cl− Important metal – insoluble salt-anion electrode Hg(l)Hg2Cl2 (s)Cl− (c): Pb(s)PbSO4 (s)SO4 2− (c): in lead-acid battery Hg2Cl2 (s) + 2e− → 2Hg(l) + 2Cl− (c) PbSO4 (s) + 2e− → Pb(s) + SO4 2− (c) There are three phases contacting with each other in the electrode. 7.6.4 Reversible electrodes §7.6 Reversible cell