1、1Chapter 3 Chapter 3 ElectrochemistryElectrochemistry電化學電化學Electrochemistry deals with chemical changes produced by an electric current and with the production of electricity by chemical changes. The applications involve in battery, electrolysis, electrorefining of metals. 電化學電化學是研究化學能與電能轉(zhuǎn)換的學科，其主要應用

2、有是研究化學能與電能轉(zhuǎn)換的學科，其主要應用有電池、電解、金屬的電化學加工等。電池、電解、金屬的電化學加工等。2Terms Used in Electrochemistry(1)Terms Used in Electrochemistry(1) 電化學術語電化學術語(1)(1) Oxidize 氧化氧化; reduce 還原還原; electric current電電流流; oxidizing agent 氧化劑氧化劑; reducing agent 還原還原劑劑; oxidation number 氧化數(shù)氧化數(shù); zinc plate 鋅板鋅板; copper strip 銅板銅板 redox

3、 氧化還原氧化還原; do work 作作功功; galvanic cell 原電池原電池; electrode 電極電極; cathode 陽極陽極; anode 陰極陰極; salt bridge 鹽橋鹽橋; 3Terms Used in Electrochemistry (2)Terms Used in Electrochemistry (2)電化學專業(yè)詞匯電化學專業(yè)詞匯(2)(2) potassium chloride 氯化鉀氯化鉀; amperemeter 安培計安培計; pointer 指針指針; zinc compartment鋅鋅半室半室; positive charge 正電

4、荷正電荷; redox couple 電對電對; cell potential 原原電池電動勢電池電動勢; volt 伏特伏特; voltmeter 伏特計伏特計; half-cell 半電池半電池; inert electrode 惰性電極惰性電極; platinum 鉑鉑; calomel electrode 甘汞電極甘汞電極; reference electrode 參比電極參比電極;4Redox ReactionsRedox Reactions 氧化還原反應氧化還原反應 Redox, the short name for oxidation-reduction, is one of 4

5、 types of chemical reactions: 氧化還原反應的縮寫為氧化還原反應的縮寫為Redox, , 是四是四種化學反應的一種。種化學反應的一種。 combination 化合反應化合反應 decomposition 分分解反應解反應 metathesis 復分解反應復分解反應 redox 氧化氧化還原反應還原反應. E.g. Zn(s) + H2SO4(aq) = ZnSO4(aq) + H2(g) Here, Zinc metal is reducing agent; sulfuric acid(H2SO4) is oxidizing agent金屬鋅作還原劑，金屬鋅作還原

6、劑，硫酸作氧化劑硫酸作氧化劑. .5Oxidizing and Reducing AgentsOxidizing and Reducing Agents氧化劑和還原劑氧化劑和還原劑1. Oxidizing Agent: 氧化劑氧化劑 The species which causes oxidation is called the oxidizing agent. The substance which is oxidized loses electrons to the other. The oxidizing agent is always reduced. 氧化劑發(fā)生氧化劑發(fā)生還原反應還原

7、反應。2. Reducing Agent: 還原劑還原劑 The species which causes reduction is called the reducing agent. The substance which is reduces gains electrons from the other. The Reducing agent is always oxidized. 還原劑發(fā)生還原劑發(fā)生氧化反應。氧化反應。6Common Reducing and Oxidizing Common Reducing and Oxidizing AgentsAgents常見氧化劑和還原劑常見

8、氧化劑和還原劑 The reduced species may be used as a reducing agent, e.g. Zinc metal, stannous chloride(SnCl2), iodine(I2), sodium thiosulfate(Na2S2O3). The oxidized species as an oxidizing agent, e.g. copper (Cu2+) ions, potassium permanganate(KMnO4), potassium dichromate(K2Cr2O7), sodium bismuthate (NaBiO

9、3).7Oxidation NumbersOxidation Numbers氧化數(shù)氧化數(shù) an atom in its elemental form (Na, O2, Cl2 ) oxidation number = 0 元素的氧化數(shù)為元素的氧化數(shù)為0。2. For a monatomic ion: oxidation number = ion charge 單原子離子的電荷等于氧化數(shù)。單原子離子的電荷等于氧化數(shù)。3. The sum of oxidation number values for the atoms in a compound equals zero. The sum of o

10、xidation number values for the atoms in a polyatomic ion equals the ion charge. 化合物的化合物的氧化數(shù)為氧化數(shù)為0，多原子離子中所有元素的氧化數(shù)之和，多原子離子中所有元素的氧化數(shù)之和等于離子電荷。等于離子電荷。 Rules for Assigning an Oxidation Number氧化數(shù)氧化數(shù)的判定的判定81. For fluorine: Ox . no. = 1 in all compounds 氟為氟為 1。2. For oxygen: Ox . no. = 1 in peroxides 過氧化物中為過

11、氧化物中為 1。Ox. No. = 2 in all other compounds (except with F) 氧化物中為氧化物中為 2。3. For Group 7A 鹵素鹵素:Ox . no. = 1 in combination with metals, nonmetals (except O) 金屬、非金屬元素鹵金屬、非金屬元素鹵化物中為化物中為 1, and other halogens lower in the group.4. For Group 1A 堿金屬堿金屬: Ox . no. = +1 in all compounds 為為+1。5. For Group 2A 堿

12、土金屬堿土金屬: Ox . no. = +2 in all compounds 為為+2。6. For hydrogen:Ox . no. = +1 in combination with nonmetals 與非金屬化合為與非金屬化合為+1，Ox . no. = 1 in combinations with metals and boron 與金屬和硼化合為與金屬和硼化合為 1。9Balancing Redox ReactionsBalancing Redox Reactions氧化還原反應的配平氧化還原反應的配平For example,KMnO4 + H2S + H2SO4 = MnSO4

13、 + S + K2SO4 + H2OMnO4 + 8H+ + 5e = Mn2+ + 4H2O 氧化劑氧化劑H2S = S + 2H+ + 2e 還原劑還原劑2 + 5 2KMnO4 +5H2S +3H2SO4 =2MnSO4 +5S +K2SO4 + 8H2O10Redox Reactions - Ion Electron Method.Redox Reactions - Ion Electron Method.離子電子法離子電子法 Under acidic condition 酸性條件酸性條件 Balance the half reaction separately except H &a

14、mp; Os.Balance Oxygen by H2O 用水分子平衡氧原子。用水分子平衡氧原子。Balance Hydrogen by H+用用H+平衡氫原子。平衡氫原子。Balance charge by e 加上電子平衡電荷。加上電子平衡電荷。 Under basic condition 堿性條件堿性條件 the same procedure as the acidic, except 處理處理如酸性條件，注意：如酸性條件，注意：Eliminate H+ by adding: H+ + OH H2O 11Examples Examples 例題例題BrO4 + CrO2 BrO3 + C

15、rO42 (basic)配平氧化劑、還原劑配平氧化劑、還原劑 ：BrO4 + e BrO3 CrO2 CrO42 + e 配平氧原子：配平氧原子： BrO4 + 2H+ + 2e BrO3 + H2O 2H2O 2H+ + 2OH BrO4 + 2H2O + 2e BrO3 + 2OH 堿性條件：堿性條件： CrO2 + 2H2O CrO42 + 4H+ + 3e 4H+ + 4OH 4H2O CrO2 + 4OH CrO42 + 2H2O + 3e總反應：總反應： 3BrO4 + 2CrO2 + 2OH + 2H2O 3BrO3 + 2CrO42 3 2+12The Activity Ser

16、ies of MetalsThe Activity Series of Metals金屬活潑程度金屬活潑程度 Metals can be placed in order of their tendencies for losing electrons. This is called the activity series.Activity series of metal in aqueous solution 水溶液水溶液中金屬的活潑性中金屬的活潑性PotassiumCalcium Sodium Magnesium Aluminum Zinc Iron Tin Nickel Lead Hydr

17、ogen Copper Silver MercuryWhat determines whether the reactions occur?13Galvanic Cells(1) Galvanic Cells(1) 原電池原電池 The redox reaction is really an electron transfer reaction電子得失電子得失. No electric current results when the oxidizing agent and reducing agent are mixed. Zn (s) + Cu2+ (aq) Zn2+ (aq) + Cu

18、(s)Zinc plate, copper sulfate zinc sulfate, copper stripZinc atomCopper atomNo useful work is obtained14Galvanic Cell(2) Galvanic Cell(2) 原電池原電池 A galvanic cell is an energy-producing apparatus, in which the oxidation and reduction reaction occur in two separate compartments, often called half-cells

19、. 原電池是將氧化還原反應原電池是將氧化還原反應的化學能轉(zhuǎn)化為電能的裝置。的化學能轉(zhuǎn)化為電能的裝置。ZnCuInitially, there is a flow of electron, after some time, the process stops because of the charge build up. 起先電子流起先電子流動，但因電荷積聚，一會兒動，但因電荷積聚，一會兒便停止便停止15Completing the circuitCompleting the circuit 鹽橋連接鹽橋連接A salt bridge, an up-side-down U tube, conta

20、ining saturated potassium chloride (KCl) solution and galatin(凝膠凝膠). An amperemeter(安安培計培計) is connected into the circuit. Therefore, the chemical energy can be converted into the electric energy.ZnCu鹽橋的作用鹽橋的作用: In order for electrons to move through an external wire, charge must not build up at any

21、 cell. This is done by the salt bridge in which ions migrate to different compartments neutralize any charge build up. 16The cathode正極正極: electrode at which electrons flow in電子流入電子流入, Copper (Cu) strip severs as the cathode.The anode負極負極: electrode at which electrons flow out電子流出電子流出, Zinc (Zn) plat

22、e serves as the anode.Reduction always occurs at the cathode 陽極發(fā)生陽極發(fā)生還原還原; oxidation always occurs at the anode 陰極陰極發(fā)生氧化發(fā)生氧化.A salt bridge works as ion flow channel, is to balance the ion charges in each compartment 鹽橋充當離子通道鹽橋充當離子通道.Potassium ions (K+) move to copper sulfate solution;whereas chlorid

23、e ions (Cl ) move to zinc sulfate solution.17Cell Assembly Cell Assembly 電池構(gòu)造電池構(gòu)造Electron transfer can occur if the circuit is closed. 電路閉合，電子流動。電路閉合，電子流動。Parts of a cell: Two conductors 兩個電極兩個電極 Electrolyte solution 電解質(zhì)溶液電解質(zhì)溶液 Salt Bridge / Porous membrane 鹽橋或多孔膜鹽橋或多孔膜Three processes must happen if

24、 e is to flow. e transport through external circuit 電子流經(jīng)外電子流經(jīng)外電路電路 In the cell, ions a must migrate 離子在電池內(nèi)遷離子在電池內(nèi)遷移移 Circuit must be closed (no charge build up) 電電路閉合，無電荷積聚。路閉合，無電荷積聚。18How a Galvanic Cell Works?How a Galvanic Cell Works?原電池工作原理原電池工作原理Anode (-)grayNegative electrode generates electro

25、nOxidation OccurCathode (+)RedPositive electrode accepts electronReduction OccurAnode/Anion (-)Cathode/Cation(+)e-Reducing Agente-e-Oxidizing AgentPorous Disk19The Diagrammatic Representation The Diagrammatic Representation of a Galvanic Cellof a Galvanic Cell原電池符號原電池符號The oxidized species and the r

26、educed species in each compartment (half-cell) consist of a redox couple 氧化還原電對氧化還原電對, written as e.g. Zn2+/Zn couple. A galvanic cell is depicted as( ) Zn | ZnSO4 (c1) | CuSO4 (c2) | Cu (+)Anode負極負極Phase boundary相界面相界面Concentration濃度濃度Salt bridgeCathode正極正極20Line Notation ConventionLine Notation Co

27、nvention電池符號電池符號Sometimes, an inert electrode is necessary. It should be a conductor導體導體 that delivers electricity and does not enter into the cell reaction. E.g. platinum and graphite. 惰性電極導惰性電極導電，但不參與電池反應，如鉑、石墨。電，但不參與電池反應，如鉑、石墨。 In hydrogen-zinc galvanic cell, platinum is used as the cathode. The

28、line notation for the H2 -Zn galvanic cell is as follows:氫氫- -鋅原電池中，鉑作正鋅原電池中，鉑作正極，電池符號極，電池符號:( ) Zn | Zn2+ (c1) | H+ (c2) | H2 (g, 1atm) | Pt (+)21Line Notation of Cell ExamplesLine Notation of Cell Examples電池符號電池符號CCrAg( ) C | I (c1), I2(g,1atm) | MnO4 (c2) , Mn2+(c3) | C (+) ( ) Cr | Cr3+ (c1) | A

29、g+(c2) | Ag (+)C22Electrode PotentialsElectrode Potentials電極電位電極電位 Electrons generated in a cell are thought to be “driven” toward the cathode by the electromotive force原電池中的電子由電動勢驅(qū)使，原電池中的電子由電動勢驅(qū)使，流向正極流向正極. Cell potential電池電動勢電池電動勢: a potential difference existing at two electrodes. 正、負極間的電勢差。正、負極間的

30、電勢差。 A voltmeter says the cell potential of Zn-Cu galvanic cell is about 1 volt. 鋅鋅-銅原電池的電動銅原電池的電動勢為勢為1伏伏. Cathode has a higher potential正極電位高正極電位高; anode has a lower potential負極電位低負極電位低, each has a potential, called electrode potential. 正、正、負極都有電位，叫作電極電位。負極都有電位，叫作電極電位。23Some Commonly Used Electrode

31、sSome Commonly Used Electrodes 常用電極常用電極 Types of ElectrodesCouples Electrodes Me-Men+electrode Zn2+/Zn Zn Zn2+ A-An-electrode Cl2/Cl Cl Cl2 Pt Redox electrode Fe3+/Fe2+ Fe3+,Fe2+ PtMe-slightly soluble salt AgCl/Ag Ag AgCl Cl Any two electrodes can build up a cell. 原電池由原電池由兩個電極構(gòu)成。兩個電極構(gòu)成。24Standard El

32、ectrode PotentialStandard Electrode Potential標準電極電位標準電極電位There is no satisfactory method to determine the actual potential of single electrode. But cell potential can be determined. So a standard electrode or reference electrode must be assigned. 單個電極的電為不可測，但單個電極的電為不可測，但電池電動勢電池電動勢可測。所以，必須指定一參考電極可測。所

33、以，必須指定一參考電極.The potential of standard hydrogen electrode is assigned as zero at standard conditions 標準狀標準狀態(tài)下的氫電極的電極電位被指定為態(tài)下的氫電極的電極電位被指定為0伏伏.For example, a cell composed of zinc electrode and hydrogen electrode, has a cell potential of 0.786 V at standard conditions. Zinc electrode behaves as anode.

34、25E cell = E cathode - - E anode E anode = - - 0.7618E (Zn2+/Zn)= - - 0.7618V H+ = 1.00 H2 (g) e-Pt gauzepH2(g) = 1.00 atm e-H2 (g) 0.76VZn1M Zn2+1M H+26Reference ElectrodeReference Electrode參比電極參比電極It is inconvenient to use standard hydrogen electrode because of use of pure hydrogen gas and the spe

35、cial treatment of the electrode. 標準標準氫電極因使用純氫、并需作特別處理，故使用不便。氫電極因使用純氫、并需作特別處理，故使用不便。Usually we use calomel electrode, which consisting of 常用的參比電極是甘汞電極，其電常用的參比電極是甘汞電極，其電池符號和結(jié)構(gòu)如下：池符號和結(jié)構(gòu)如下：When using saturated KCl solution 使用飽和氯使用飽和氯化鉀溶液時，其電位化鉀溶液時，其電位:E甘汞電極甘汞電極o = 0.2415VPt Hg Hg2Cl2 Cl- -27Potential Va

36、lues of Some ElectrodesPotential Values of Some Electrodes 一些電極的電極電位一些電極的電極電位Couples Electrode Reactions Electrode potentials K+/K K+eK 2.931Zn2+/Zn Zn2+2e Zn 0.7618H+/H 2H+2eH2 0.0000Cu2+/Cu Cu2+2eCu +0.3419F2/F F2+2e2F +2.866電對電對 電極反應電極反應 電極電位電極電位28Table of Electrode Potentials電極電位表電極電位表In the tab

37、le, from the top to the bottom, the algebraic value of as electrode potentials increases; the reduced species of an electrode is a less stronger reducing agent; and the oxidized species of an electrode is a much stronger oxidizing agent. 表中，上方電對的還原型物質(zhì)為還原劑，下方電對的表中，上方電對的還原型物質(zhì)為還原劑，下方電對的氧化型物質(zhì)為氧化劑。自上而下，電

38、極電位增加。氧化型物質(zhì)為氧化劑。自上而下，電極電位增加。還原型物質(zhì)的還原性降低，而氧化型物質(zhì)的氧化性還原型物質(zhì)的還原性降低，而氧化型物質(zhì)的氧化性增強。增強。 電極電位最低的是電極電位最低的是Li+/Li，但金屬鋰不是最活潑的，但金屬鋰不是最活潑的，為什么？為什么？29Meanings of the Standard Electrode PotentialMeanings of the Standard Electrode Potential標準電極電位的意義標準電極電位的意義If an electrode has a large negative potential, the reduced

39、species of the electrode is most easily oxidized電極電位愈小，其還原電極電位愈小，其還原型物質(zhì)愈易被氧化型物質(zhì)愈易被氧化. If an electrode has a large positive potential, the oxidized species is a strong oxidizing agent電極電位愈正，其氧化型物質(zhì)是強氧化電極電位愈正，其氧化型物質(zhì)是強氧化劑劑.30Use of the Table of Standard Electrode Use of the Table of Standard Electrode P

40、otentials(1) Potentials(1) 電極電位表的使用電極電位表的使用 the potentials are standard reduction potentials 表中為還原電位表中為還原電位. No matter how differently the electrode reaction is written, the standard electrode potential doesnt vary 標準電極電位的數(shù)值與電標準電極電位的數(shù)值與電極反應的寫法無關極反應的寫法無關.or Zn 2e Zn2+Zn2+ + 2e ZnE (Zn2+/Zn)= - - 0.76

41、18V31Use of the Table of Standard Electrode Use of the Table of Standard Electrode Potentials(2)Potentials(2) the electrode potential keeps the same with the change in stiochoimetric numbers of the electrode reaction 電極電位的數(shù)值并不隨電極反應電極電位的數(shù)值并不隨電極反應的計量系數(shù)的變化而變化的計量系數(shù)的變化而變化. O2 + 2H2O + 4e 4OH or 1/2O2 + H

42、2O + 2e 2OH The electrode potentials are the characteristic values. 電極電位是電極的特征值。電極電位是電極的特征值。 some electrodes may have different potentials in different media. 有些電極在不同介質(zhì)中的電極電有些電極在不同介質(zhì)中的電極電位的數(shù)值有所不同位的數(shù)值有所不同.E (O2 /OH )= 0.401V32Nernst EquationNernst Equation 能斯特方程式能斯特方程式For an electrode reaction, 就如下的電

43、極反應就如下的電極反應 Oxidized form + ne Reduced form c/ )Ox(c/c)dRec(lnnFRTEEAt 25: c/ )Ox(c/c)dRec(lgn0529. 0EE33ExamplesFor example, O2 + 2H2O + 4e 4OH Nernst equation: 能斯特方程式能斯特方程式 p/pOHlg40529. 0)OH/O(E)OH/O(E2O422 MnO4 + 8H+ + 5e Mn2+ + 4H2O Nernst equation: 84224HMnOMnlg50529. 0E)Mn/MnO(E 34Using Nerns

44、t Equation n represents the number of electrons gained or lost得失電子數(shù)得失電子數(shù)n. the stiochoimetric number in a half-reaction is the number of power in the c(Ox) or c(Red)半反應的計量系數(shù)為能斯特方程式中的濃度的方次半反應的計量系數(shù)為能斯特方程式中的濃度的方次數(shù)數(shù). the relative concentration of a gas is expressed in the partial pressure 氣體的濃度以氣體的濃度以分壓

45、表示分壓表示. pure solids and liquids are not included 固體固體和純液體不計和純液體不計.35ExampleExample: calculate the potential for permanganate / manganese ion couple in neutral solution.Solution: MnO4 + 8H+ + 5e Mn2+ + 4H2O using Nernst equation: 84224HMnOMnlg50529. 0E)Mn/MnO(E 91. 01011lg50529. 051. 1)Mn/MnO(E8724 S

46、uppose MnO4 =1 mol L 1, Mn2+ = 1 mol L 1 36Temperature(2) Temperature has little impact on the electrode potentials. 溫度對溫度對電極電位的影響電極電位的影響甚微。甚微。37Relationship between Relationship between r rGGmm and Cell and Cell PotentialsPotentials r rGGmm 與電動勢之間的關系與電動勢之間的關系電功電功rGm=Wmaxwe know Wmax= - - QE = - - n

47、FE the cell potentials can be used to judge the spontaneity of a redox reaction. 電池電動勢可判斷電池電動勢可判斷氧化還原反應的自發(fā)性：氧化還原反應的自發(fā)性：E 0 nonspontaneous; 非自發(fā)非自發(fā)E =0 G =0 at equilibrium; 可逆可逆E 0 G 0 spontaneous 自發(fā)自發(fā)orrGm= - - nFErGm = - - nFE 38Example: c(Pb2+)=0.1mol.L-1, c(Sn2+)=1.0mol.L-1. Predictthe direction f

48、or the reaction of Pb2+ Sn = Sn2+ Pb= -= -0.1262 - - 0.0296 = - = -0.1558VWhereas, E(Sn2+/Sn) = E (Sn2+/Sn)= - -0.1375V.Comparing the two potentials 比較正、負極比較正、負極 的電極電的電極電位位, E(Pb2+/Pb) E (Sn2+/Sn) Sn2+Sn acts as cathode正極正極, Pb2+Pb acts as anode負負極極. The reverse reaction is spontaneous 逆反應自發(fā)逆反應自發(fā).1

49、. 01lg20529. 01262. 0Pb1lg20529. 0E)Pb/Pb(E22 Solution: using Nernst equation, 利用能斯特方程式利用能斯特方程式39Using Electrode PotentialsUsing Electrode Potentials(1) judge whether the electrode is cathode or anode. 推推測哪個電極為正極、哪個為負極。測哪個電極為正極、哪個為負極。 Cathode: reduction reaction occurs 正極發(fā)生還原。正極發(fā)生還原。 has a high pote

50、ntial 電位高。電位高。 Anode: oxidation reaction occurs 負極發(fā)生氧化。負極發(fā)生氧化。 has a low potential 電位低。電位低。Example: if a cell is composed of the following electrodes, (1) Zn Zn2+（1.0mol.L-1) (2) Zn Zn2+(0.001mol.L-1)Point out the cathode and anode and calculate the cell potential. 指出正、負極，并計算電動勢。指出正、負極，并計算電動勢。40Solu

51、tion: for electrode (2), using Nernst equation,E2(Zn2+/Zn)=001.01lg20592.0E For electrode (1), E1(Zn2+/Zn) = E = 0.7618VComparing the two potentials, E2 E1, thus, Electrode (1) acts as cathode 電極電極1為正極為正極; electrode (2)acts as anode 電極電極2作負極作負極. The cell potential of both electrodes is 電動勢為電動勢為 E =

52、= E+ + - - E- - = = E1 1 - - E2 2= = 0.089V This cell is called concentration cell 該電池為該電池為濃差電池濃差電池.= - -0.8506V41(2) Calculating cell Potentials 計算電動勢計算電動勢 (3) compare the redox ability of oxidizing agents and reducing agents 比較氧化劑、還原劑的氧化還原能力比較氧化劑、還原劑的氧化還原能力E = E+ E -Example: Couples電對電對: I2/I- -，

53、Br2/Br- -， Fe3+/Fe2+ E /V: 0.5355, 1.066, 0.771Compare the redox ability of the three couples.Solution: oxidizing abilities decrease 氧化能力下降氧化能力下降: Br2 Fe3+ I2reducing abilities increase 還原能力增強還原能力增強: I- - Fe2+ Br- -42Predicate the Spontaneity of a RedoxPredicate the Spontaneity of a Redox預測反應的自發(fā)性預測反

54、應的自發(fā)性Example: Silver is an inert element. It cannot react with dilute sulfuric or hydrochloric acid to evolve the hydrogen gas. When silver is dipped into the 1.0 M hydroiodic acid solution, predicate the spontaneity of the reaction, 銀是惰性元素，它銀是惰性元素，它不能與稀硫酸或稀鹽酸作用，產(chǎn)生氫氣。若銀與不能與稀硫酸或稀鹽酸作用，產(chǎn)生氫氣。若銀與1.0 mol

55、L 1 HI反應，計算說明如下反應的方向反應，計算說明如下反應的方向. Ag + 2HI AgI + H2 (Ksp AgI = 8.3 10 17, EAg+/Ag = 0.799 V)Solution: in the reaction, anode is負極為負極為 AgI + e Ag + I ; cathode is 正極是正極是 2H+ + 2e H2 43Ag1logn059. 0EEAg/AgAg/Ag For the Ag+/Ag couple, its nernst equation, 銀電極銀電極的能斯特方程式的能斯特方程式For the AgI/Ag couple, it

56、s nernst equation, 碘化銀碘化銀/銀電極的能斯特方程式銀電極的能斯特方程式: AgI + e Ag + I ;Ilogn059. 0EEAg/AgIAg/AgI Rewrite the the nernst equation of Ag+/Ag couple 改寫改寫Ag+/Ag的能斯特方程式的能斯特方程式: IAgIlogn059. 0EEAg/AgAg/Ag If there exist the equilibrium now, 若溶液中有平衡若溶液中有平衡:44AgI(s) Ag+(aq) + I (aq) in the Ag+/Ag couple, there has

57、 Ag I = Ksp (AgI) 則銀電極的能斯特方程式可寫為則銀電極的能斯特方程式可寫為: )AgI(KIlogn059. 0EEspAg/AgAg/Ag The value of “Ag+/Ag” electrode potential, 代入數(shù)代入數(shù)據(jù)，據(jù)，“銀電極銀電極”的電極電位的電極電位: Ilog15. 0103 . 8Ilog1059. 0799. 0E17Ag/Ag 比較上式和比較上式和碘化銀碘化銀/銀銀電極的能斯特方程式，可得電極的能斯特方程式，可得:V15. 0EAg/AgI 0EE2H/HAg/AgI 反應可進行。反應可進行。有氫氣釋放。有氫氣釋放。45If an o

58、xidizing agent, for instance, KMnO4, reacts with them, the readiness of the reaction is: 如如KMnO4與它們與它們 作用，作用， I- - Fe2+ Br- -If an reducing agent, for instance, Zn, reacts with them, the readiness of the reaction is: 鋅與它們作用鋅與它們作用 Br2 Fe3+ I2(4) predicate the extent of a redox reaction 預測反應進度預測反應進度At

59、 equilibrium 平衡時平衡時G =0 - -rGm = RT ln K at 298.15K- -rGm = RT ln K - -rGm = nFE電池電池 0592.0nEKlg 46CalculationSo, the cell potential, E電池電池 = - = - 0.771V Example: Calculate the equilibrium constant for the reaction.計算如下反應的平衡常數(shù)。計算如下反應的平衡常數(shù)。2H+2Fe2+H2+2Fe3+Solution: E (H+/H2)= 0 V E (Fe3+/Fe2+) = 0.7

60、71V05.260529. 0)771. 0(20529. 0nEKlg 電電池池K = = 8.9110 -2747Electrode Potential or Latime DiagramElectrode Potential or Latime Diagram元素電位圖元素電位圖Cu2+ Cu+ Cu0.1670.522Electrode potential Diagram of an element元素電位元素電位圖圖: the diagrammatic representation of potentials in relationship to all oxidation states o