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Page 1 ELECTROCHEMISTRY ELECTRODE POTENTIAL For any electrode ? oxidiation potential = ? Reduction potential E cell = R.P of cathode ? R.P of anode E cell = R.P. of cathode + O.P of anode E cell is always a +ve quantity & Anode will be electrode of low R.P Eº Cell = SRP of cathode ? SRP of anode. ? Greater the SRP value greater will be oxidising power. GIBBS FREE ENERGY CHANGE : ?G = ? nFE cell ?Gº = ? nFEº cell NERNST EQUATION : (Effect of concentration and temp on emf of cell) ?G = ?Gº + RT ?nQ (where Q is raection quotient) ?Gº = ? RT ?n K eq E cell = Eº cell ? nF RT ?n Q E cell = Eº cell ? Q log nF RT 303 . 2 Page 2 ELECTROCHEMISTRY ELECTRODE POTENTIAL For any electrode ? oxidiation potential = ? Reduction potential E cell = R.P of cathode ? R.P of anode E cell = R.P. of cathode + O.P of anode E cell is always a +ve quantity & Anode will be electrode of low R.P Eº Cell = SRP of cathode ? SRP of anode. ? Greater the SRP value greater will be oxidising power. GIBBS FREE ENERGY CHANGE : ?G = ? nFE cell ?Gº = ? nFEº cell NERNST EQUATION : (Effect of concentration and temp on emf of cell) ?G = ?Gº + RT ?nQ (where Q is raection quotient) ?Gº = ? RT ?n K eq E cell = Eº cell ? nF RT ?n Q E cell = Eº cell ? Q log nF RT 303 . 2 E cell = Eº cell ? n 0591 . 0 log Q [At 298 K] At chemical equilibrium ?G = 0 ; E cell = 0. ? log K eq = 0591 . 0 E n o cell . Eº cell = n 0591 . 0 log K eq For an electrode M(s)/M n+ . nF RT 303 . 2 º E E M / M M / M n n ? ? ? ? log ] M [ 1 n? . CONCENTRATION CELL : A cell in which both the electrods are made up of same material. For all concentration cell Eº cell = 0. (a) Electrolyte Concentration Cell : eg. Zn(s) / Zn 2+ (c 1 )  Zn 2+ (c 2 ) / Zn(s) E = 2 0591 . 0 log 1 2 C C (b) Electrode Concentration Cell : eg. Pt, H 2 (P 1 atm) / H + (1M) / H 2 (P 2 atm) / Pt E = 2 0591 . 0 log ? ? ? ? ? ? ? ? 2 1 P P DIFFERENT TYPES OF ELECTRODES : 1. MetalMetal ion Electrode M(s)/M n+ . M n+ + ne ? ?? ? M(s) E = Eº + n 0591 . 0 log[M n+ ] 2. Gasion Electrode Pt /H 2 (Patm) /H + (XM) as a reduction electrode H + (aq) + e ? ?? ? 2 1 H 2 (Patm) E = Eº ? 0.0591 log ] H [ P 2 1 H 2 ? Page 3 ELECTROCHEMISTRY ELECTRODE POTENTIAL For any electrode ? oxidiation potential = ? Reduction potential E cell = R.P of cathode ? R.P of anode E cell = R.P. of cathode + O.P of anode E cell is always a +ve quantity & Anode will be electrode of low R.P Eº Cell = SRP of cathode ? SRP of anode. ? Greater the SRP value greater will be oxidising power. GIBBS FREE ENERGY CHANGE : ?G = ? nFE cell ?Gº = ? nFEº cell NERNST EQUATION : (Effect of concentration and temp on emf of cell) ?G = ?Gº + RT ?nQ (where Q is raection quotient) ?Gº = ? RT ?n K eq E cell = Eº cell ? nF RT ?n Q E cell = Eº cell ? Q log nF RT 303 . 2 E cell = Eº cell ? n 0591 . 0 log Q [At 298 K] At chemical equilibrium ?G = 0 ; E cell = 0. ? log K eq = 0591 . 0 E n o cell . Eº cell = n 0591 . 0 log K eq For an electrode M(s)/M n+ . nF RT 303 . 2 º E E M / M M / M n n ? ? ? ? log ] M [ 1 n? . CONCENTRATION CELL : A cell in which both the electrods are made up of same material. For all concentration cell Eº cell = 0. (a) Electrolyte Concentration Cell : eg. Zn(s) / Zn 2+ (c 1 )  Zn 2+ (c 2 ) / Zn(s) E = 2 0591 . 0 log 1 2 C C (b) Electrode Concentration Cell : eg. Pt, H 2 (P 1 atm) / H + (1M) / H 2 (P 2 atm) / Pt E = 2 0591 . 0 log ? ? ? ? ? ? ? ? 2 1 P P DIFFERENT TYPES OF ELECTRODES : 1. MetalMetal ion Electrode M(s)/M n+ . M n+ + ne ? ?? ? M(s) E = Eº + n 0591 . 0 log[M n+ ] 2. Gasion Electrode Pt /H 2 (Patm) /H + (XM) as a reduction electrode H + (aq) + e ? ?? ? 2 1 H 2 (Patm) E = Eº ? 0.0591 log ] H [ P 2 1 H 2 ? 3. Oxidationreduction Electrode Pt / Fe 2+ , Fe 3+ as a reduction electrode Fe 3+ + e ? ?? ? Fe 2+ E = Eº ? 0.0591 log ] Fe [ ] Fe [ 3 2 ? ? 4. MetalMetal insoluble salt Electrode eg. Ag/AgCl, Cl ? as a reduction electrode AgCl(s) + e ? ?? ? Ag(s) + Cl ? Ag / AgCl / Cl E ? = Ag / AgCl 0 / Cl E ? ? 0.0591 log [Cl ? ]. ELECTROLYSIS : (a) K + , Ca +2 , Na + , Mg +2 , Al +3 , Zn +2 , Fe +2 , H + , Cu +2 , Ag + , Au +3 . Increasing order of deposition. (b) Similarly the anion which is strogner reducing agent(low value of SRP) is liberated first at the anode. diposition of order g sin Increa , Br , Cl , OH , NO , SO ? ? ? ? 3 ? 2 4 ? ? ? ? ? ? ? ? ? ? ? ? ? I FARADAY?S LAW OF ELECTROLYSIS : First Law : w = zq w = Z it Z = Electrochemical equivalent of substance Second Law : W ? E E W = constant .......... E W E W 2 2 1 1 ? ? 96500 factor efficiency current t i E W ? ? ? . Current efficiency = 100 produced deposited/ mass l Theoritica produced deposited/ mass actual ? CONDITION FOR SIMULTANEOUS DEPOSITION OF Cu & Fe AT CATHODE Cu / Cu 2 º E ? 2 0591 . 0 ? log ? 2 Cu 1 = Fe / Fe 2 º E ? ? 2 0591 . 0 log ? 2 Fe 1 Condition for the simultaneous deposition of Cu & Fe on cathode. CONDUCTANCE : ? Conductance = ce tan sis Re 1 Page 4 ELECTROCHEMISTRY ELECTRODE POTENTIAL For any electrode ? oxidiation potential = ? Reduction potential E cell = R.P of cathode ? R.P of anode E cell = R.P. of cathode + O.P of anode E cell is always a +ve quantity & Anode will be electrode of low R.P Eº Cell = SRP of cathode ? SRP of anode. ? Greater the SRP value greater will be oxidising power. GIBBS FREE ENERGY CHANGE : ?G = ? nFE cell ?Gº = ? nFEº cell NERNST EQUATION : (Effect of concentration and temp on emf of cell) ?G = ?Gº + RT ?nQ (where Q is raection quotient) ?Gº = ? RT ?n K eq E cell = Eº cell ? nF RT ?n Q E cell = Eº cell ? Q log nF RT 303 . 2 E cell = Eº cell ? n 0591 . 0 log Q [At 298 K] At chemical equilibrium ?G = 0 ; E cell = 0. ? log K eq = 0591 . 0 E n o cell . Eº cell = n 0591 . 0 log K eq For an electrode M(s)/M n+ . nF RT 303 . 2 º E E M / M M / M n n ? ? ? ? log ] M [ 1 n? . CONCENTRATION CELL : A cell in which both the electrods are made up of same material. For all concentration cell Eº cell = 0. (a) Electrolyte Concentration Cell : eg. Zn(s) / Zn 2+ (c 1 )  Zn 2+ (c 2 ) / Zn(s) E = 2 0591 . 0 log 1 2 C C (b) Electrode Concentration Cell : eg. Pt, H 2 (P 1 atm) / H + (1M) / H 2 (P 2 atm) / Pt E = 2 0591 . 0 log ? ? ? ? ? ? ? ? 2 1 P P DIFFERENT TYPES OF ELECTRODES : 1. MetalMetal ion Electrode M(s)/M n+ . M n+ + ne ? ?? ? M(s) E = Eº + n 0591 . 0 log[M n+ ] 2. Gasion Electrode Pt /H 2 (Patm) /H + (XM) as a reduction electrode H + (aq) + e ? ?? ? 2 1 H 2 (Patm) E = Eº ? 0.0591 log ] H [ P 2 1 H 2 ? 3. Oxidationreduction Electrode Pt / Fe 2+ , Fe 3+ as a reduction electrode Fe 3+ + e ? ?? ? Fe 2+ E = Eº ? 0.0591 log ] Fe [ ] Fe [ 3 2 ? ? 4. MetalMetal insoluble salt Electrode eg. Ag/AgCl, Cl ? as a reduction electrode AgCl(s) + e ? ?? ? Ag(s) + Cl ? Ag / AgCl / Cl E ? = Ag / AgCl 0 / Cl E ? ? 0.0591 log [Cl ? ]. ELECTROLYSIS : (a) K + , Ca +2 , Na + , Mg +2 , Al +3 , Zn +2 , Fe +2 , H + , Cu +2 , Ag + , Au +3 . Increasing order of deposition. (b) Similarly the anion which is strogner reducing agent(low value of SRP) is liberated first at the anode. diposition of order g sin Increa , Br , Cl , OH , NO , SO ? ? ? ? 3 ? 2 4 ? ? ? ? ? ? ? ? ? ? ? ? ? I FARADAY?S LAW OF ELECTROLYSIS : First Law : w = zq w = Z it Z = Electrochemical equivalent of substance Second Law : W ? E E W = constant .......... E W E W 2 2 1 1 ? ? 96500 factor efficiency current t i E W ? ? ? . Current efficiency = 100 produced deposited/ mass l Theoritica produced deposited/ mass actual ? CONDITION FOR SIMULTANEOUS DEPOSITION OF Cu & Fe AT CATHODE Cu / Cu 2 º E ? 2 0591 . 0 ? log ? 2 Cu 1 = Fe / Fe 2 º E ? ? 2 0591 . 0 log ? 2 Fe 1 Condition for the simultaneous deposition of Cu & Fe on cathode. CONDUCTANCE : ? Conductance = ce tan sis Re 1 ? Specific conductance or conductivity : (Reciprocal of specific resistance) K = ? 1 K = specific conductance ? Equivalent conductance : Normality 1000 K E ? ? ? unit : ohm ?1 cm 2 eq ?1 ? Molar conductance : Molarity 1000 K m ? ? ? unit : ohm ?1 cm 2 mole ?1 specific conductance = conductance × a ? KOHLRAUSCH?S LAW : Variation of ? eq / ? M of a solution with concentration : (i) Strong electrolyte ? M c = ? ? M ? b c (ii) Weak electrolytes : ? ? = n + ? ? ?? + n ? ?? ? ? where ? is the molar conductivity n + = No of cations obtained after dissociation per formula unit n ? = No of anions obtained after dissociation per formula unit APPLICATION OF KOHLRAUSCH LAW : 1. Calculation of ? 0 M of weak electrolytes : ? 0 M (CH3COOHl) = ? 0 M(CH3COONa) + ? 0 M(HCl) ? ? 0 M(NaCl) 2. To calculate degree of diossociation of a week electrolyte ? = 0 m c m ? ? ; K eq = ) 1 ( c 2 ? ? ? 3. Solubility (S) of sparingly soluble salt & their K sp ? M c = ? M ? = ? × ility lub so 1000 K sp = S 2 . Transport Number : t c = ? ? ? ? ? ? ? ? ? ? a c c , t a = ? ? ? ? ? ? ? ? ? ? c a a . Where t c = Transport Number of cation & t a = Transport Number of anionRead More

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