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Chapter 7 Electrochemistry 7.1 Thermodynamic Properties of Electrolyte Solutions 7.1.1 Electrolyte Strong electrolyte Weak el ectrolyte Real electrolyte Potential electrolyte NaNO 3 z + = 1 | z - |= 1 1-1 ; BaSO 4 z + = 2 | z - |= 2 2-2 ; Na 2 SO 4 z + = 1 | z - |= 2 1-2 ; Ba(NO 3 ) 2 z + = 2 | z - |= 1 2-1 。
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7.1.2 Chemical Potential of Electrolyte and Ions B = + + +
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d T=0, d p=0, d n A =0 B = + + +
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7.1.3 Activity and Activity Coefficient ideal solution real solution
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7.1.4 Mean Activity of Ions and Mean Activity Coefficients
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7.1.5 The Debye - Hückel Limiting Law Ionic atmosphere
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H2OH2O b<0.01 ~ 0.001mol·kg -1 I — Ionic Strength
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7.1.6 Ionic Strength I<0.01mol·kg -1
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7.2 Conductive Properties of Electrolyte Solutions 7.2.1 Conductance G Conductance;unit Simens S , 1S=1Ω -1 。 Resistivity ; Ω ·m. Conductivity ; S·m -1. =K (l/A) G K Cell constant
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7.2.2 Molar Conductance Λ m unit S · m 2 · mol -1 。 Λ m (K 2 SO 4 )= 0.02485 S·m 2 ·mol -1 Λ m ( K 2 SO 4 )= 0.01243 S · m 2 · mol -1
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7.2.3 Concentration dependence of and Λ m k/(S m -1 ) H 2 SO 4 KOH KCl MgSO 4 CH 3 COOH 0145 10 c/(mol dm -3 ) 20 40 60 80 c m c 400 300 200 100 m /(S cm 2 mol -1 ) HCl NaOH AgNO 3 CH 3 COOH 0 0.5 1.0 1.5 c B =0 molar conductivity of infinite dilution
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7.2.4 Independent Migration of Ion 7.2.5. Electrolytic Equilibrium of Weak Electrolytes At equilibrium
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a u = u b u /b =( 1-α ) u b/b HOAc H + + OAc -
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7.3 Electrochemical system + + + + + + + + + + Metal + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
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+ + + + + + + + + + Metal 1Metal 2 Contact potential
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Liquid-junction potential (diffusion potential) + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + ++ + + + + + + + + + + + + + + +
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7.4 Equilibrium electrochemistry 7.4.1 Reversible cell (1) Electrode reactions and cell reaction are reversible (2) I 0 (equilibrium)
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7.4.2 The Cell Potentials of Reversible Cell
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7.4.3 The Nernst Equation ---Standard Cell Potentials
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7.4.4 Standard Electrode Potential Standard Hydrogen Electrode ---SHE H + [a(H + ) =1 ] | H 2 (p =100kPa) | Pt E =0 SHE electrode in question (reduction)
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Table 11-1 25 ℃时某些电极的标准电极电势 (p = 100kPa) 电极电极反应(还原) E /V K+KK+K K + + e - == K-2.924 Na + Na Na + + e - == Na-2.7107 Mg 2+ Mg Mg 2+ + 2e - == Mg -2.375 Mn 2+ Mn Mn 2+ + 2e - == Mn -1.029 Zn 2+ Zn Zn 2+ + 2e - == Zn -0.7626 Fe 2+ Fe Fe 2+ + 2e - == Fe -0.409 Co 2+ Co Co 2+ + 2e - == Co -0.28 Ni 2+ Ni Ni 2+ + 2e - == Ni -0.23 Sn 2+ Sn Sn 2+ +2e - == Sn -0.1362 Pb 2+ Pb Pb 2+ +2e - == Pb -0.1261 H + H 2 Pt H + +e - == 1/2H 2 -0.0000( 定义量 ) Cu 2+ Cu Cu 2+ +2e - == Cu +0.3402 Cu + Cu Cu + +e - == Cu +0.522
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Hg 2 2+ Hg Hg 2+ +2e - ==Hg+0.851 Ag + Ag Ag + +e - == Ag+0.7991 OH - O 2 Pt 1/2O 2 +H 2 O+2e - ==2OH - +0.401 H + O 2 Pt O 2 +4H + + 2e - ==H 2 O+1.229 I - I 2 Pt 1/2I 2 + e - == I - +0.535 Br - Br 2 Pt 1/2Br 2 + e - ==Br - +1.065 Cl - Cl 2 Pt 1/2Cl 2 + e - == Cl - +1.3586 I - AgI Ag AgI + e - ==Ag+I - -0.1517 Br - AgBr Ag AgBr + e - ==Ag+Br - +0.0715 Cl - AgCl Ag AgCl + e - ==Ag+Cl - +0.2225 Cl - Hg 2 Cl 2 Hg Hg 2 Cl 2 + 2e - == 2Hg+2Cl - +0.2676 OH - Ag 2 O Ag Ag 2 O+2e - ==2Ag+2OH - +0.342 SO 4 2- Hg 2 SO 4 Hg Hg 2 SO 4 +2e - == 2Hg+2SO 4 2- +0.6258 SO 4 2- PbSO 4 Pb PbSO 4 + 2e - == Pb +SO 4 2- -0.356
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Oxidation state + 2e - Reduction state E MF = E (R, Reduction)- E (L, Reduction) Cl - - (a) | Cl 2 | Pt : For example
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7.5 Application of E MF Measurements 7.5.1 Determination of thermodynamics quantities Δ r G m,Δ r S m andΔ r H m Δ r G m = - zFE MF Temperature coefficient of cell
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7.5.2 Determination of γ ±
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7.5.3 Determination of pH H + | Q , QH 2 | Pt Q [ a(Q) ] +2H + [ a(H + )]+2e - QH 2 [ a(QH 2 ) ] 25 ℃, E = (0.6997 - 0.05916pH) V Q HO - - OH QH 2 Q QH 2 a ( Q)≈a(QH 2 ) Pt | H 2 (p ) | solution(pH=x) | KCl (a) | Hg 2 Cl 2 | Hg
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7.5.4 Determination of K and K sp 7.5.5 Determination of reaction direction Δ r G m = - ZFE MF < 0
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7.6 kinetics of electrochemical system 7.6.1 Rate of electrochemical reaction M + + e - M ca ca EcEc EaEa M a ca c M + +e M Cathode process υ c ; anode process υ a ;
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v - Rate of electrochemical reaction mol m -2 s -1 Current density j j=ZFυ j 0 :exchange current density
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7.6.2 Polarization and Overpotential { a}{ a} { c,e } { a,e } { c}{ c} { e}{ e}{ } { a}{ a} { c}{ c} {j}{j} (a) electrolytic cell { }{ } { a}{ a} { a,e } { c,e } { c}{ c} { e}{ e}{ } {j}{j} (b)chemical electric source { c}{ c} { a}{ a} { }{ } polarization curve Overpotential : η a — anode overpotential η c — anode overpotential
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(1). Diffusion overpotential Ag + c0c0 c'c' Diffusion layer Ag M + + e - M (2). Electrochemical overpotential
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7.6.3 Electrolytic cell (- ) Pt | H 2 | OH - ( H 2 O )| O 2 (p) | Pt ( + ) H2H2 O2O2 H2OH2OH2OH2O PtPt PtPt anode(+)cathode(-) + — I Power supply
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Pt A V R KOH 外电源 电阻 伏特计 电流计 + _ KOH VdVd V II Decomposition voltage Theory decomposition voltage Real decomposition voltage Δ (real)=Δ (theory) + (η a + | η c | ) + IR
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7.7 Power production and corrosion 7.7.1 Dry Cell Zn | NH 4 Cl | MnO 2 | C Negative electrode : Zn + 2NH 4 Cl Zn(NH 3 ) 2 Cl 2 + 2H + + 2e - positive electrode : 2MnO 2 + 2H + + 2e - 2MnOOH Cell reaction : Zn + 2MnO 2 + 2NH 4 Cl Zn(NH 3 ) 2 Cl 2 + 2MnOOH
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11.7.2 Storage Cell Pb | H 2 SO 4 (ρ = 1.28g cm -3 ) | PbO 2 Negative electrode : Pb + H 2 SO 4 PbSO 4 + 2H + + 2e - positive electrode : PbO 2 + H 2 SO 4 + 2H + + 2e - PbSO 4 + 2H 2 O Cell reaction : PbO 2 + Pb + 2H 2 SO 4 2PbSO 4 + 2H 2 O
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11.7.3.Silver-zinc Cell Zn | KOH(ω B = 0.40) | Ag 2 O | Ag Negative electrode: 2Zn + 4OH - 2Zn(OH) 2 + 4e - positive electrode : Ag 2 O 2 + 2H 2 O + 4e - 2Ag + 4OH - Cell reaction : 2Zn + Ag 2 O 2 + 2H 2 O 2Ag + 2Zn(OH) 2
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7.7.4. Fuel cell M | H 2 (g) | KOH | O 2 (g) | M
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Efficiency of Chemical Electric Source
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7.7.5 Electrochemical corrosion
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M+M+ 2H + H2H2 2e M M+M+ 2H + H2H2 2e M1M1 M2M2 Anode process : Fe Fe 2 + +2e - Cathode process : (i) 2H + +2e - H 2 ↑ (ii) O 2 +4H + +4e - 2H 2 O (i) cell reaction : Fe+2H + Fe 2 + +H 2 (ii) cell reaction : Fe+(1/2)O 2 +2H + Fe 2+ +H 2 O
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{ )} S I { c,e } { a,e }
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