Tiêu đề 03. ELECTROCHEMISTRY.pdf ✅

Anion Cation Anion Cation Electrodes Electrolyte Salt Bridge Electrical Properties Qualitative aspect depend on Device converting electrical energy into chemical energy. Anode → + vely charged; oxidation occurs Cathode → - vely charged; Reduction occurs Cell representation Oxidation half Reduction half To determine Λm & Λeq of weak electrolyt -es at infinite dilution. To calculate degree of dissociatio -n: (∝) To calculate dissociation constant of weak Electrolyt e: Λ ∝ = Λ c m 0 m Kohlrausch's law of Independent Migration of Ions At infinite dilution the molar conductivity of electrolytic is given by sum of ionic conductivities of cation & anions. Λ = ν λ + ν λ + + − − 0 0 0 m 0 • For reaction: M + + ne- M(s) + = ° − 2.303 RT 1 E E log F [M ] n n Nernst Equation • For reaction: aA + bB cC + dD = ° − c d cell cell a b 2.303 RT [C] [D] E E log nF [A] [B] • A Equilibrium Ecell = 0 ° = cell c 2.303 RT E log K nF ∆ = ∆ = − G FE or G nFE cell cell • n n n [reaction occurs only once cannot be reuse] [Can be reacharged by parring current f in opposite direction.] [Primary] [Secondary] Battery Lead storage battery Ni-cd cell Leclanche cell (dry cell) Mercury Anode: Z -Hg Cathode: Paste HgO & C Electrolyte: Paste of KOH + Pb Pb + PBO H SO (38% by loss) Z Graphite Powdered M O + C + Paste of NH4Cl + Z Cl Corrosion Example • Rusting of iron. • Furnishing of Silver. Prevention Also known as Deniel Cell: Cathode: Copper Anode: Zinc Salt bridge: Agar-Agar Electrolyte: Z SO , CuSO Cell reaction: Z + CuSO4 Z SO4 + Cu Cell representation: Z (s)| Z SO (Sol) || CuSO (sol) | Cu (s) Reduction Half-Reaction E°(V) Stronger oxidizing agent F2 (g) + 2e− → 2F− (aq) 2.87 Weaker reducing agent H2 O2 (aq) + 2H+ (aq) + 2e− → 2 H2 O (l) 1.78 MnO4 − (aq) + 8H+ (aq) + 5e− → Mn2+(aq) + 4H2 O(l) 1.51 Cl2 (g) + 2e− → 2Cl− (aq) 1.36 Cr2 O2 2− (aq) + 14 H+ (aq) + 6e− → 2Cr3+ (aq) + 7H2 O (l) 1.33 O2 (g) + 4H+ (aq) + 4e− → 2H2 O(l) 1.23 Br2 (aq) + 2e− → 2Br− (aq) 1.09 Ag+ (aq) + e− → Ag(s) 0.80 Fe3+(aq) + e− → 2Fe2+ (aq) 0.77 O2 (g) + 2H+ (aq) + 2e− → H2 O2 (aq) 0.70 I 2 (s) + 2e− → 2I− (aq) 0.54 O2 (g) + 2H2 O(l) + 4e− → 4OH− (aq) 0.40 Cu2+(aq) + 2e− → Cu(s) 0.34 SN4+(aq) + 2e− → Sn2+(aq) 0.15 2H+ (aq) + 2e− → H2 (g) 0 Pb2 +(aq) + 2e− → Pb(s) − 0.13 Ni2+(aq) + 2e− → Ni(s) − 0.26 Cd2+(aq) + 2e− → Cd(s) − 0.40 Fe2+(aq) + 2e− → Fe(s) 0.45 Zn2+(aq) + 2e− → Zn(s) − 0.76 2H2 O(l) + 2e− → H2(g) + 2OH− (aq) − 0.83 Al3+(aq) + 3e− → Al(s) 1.66 Weaker oxidizing agent Mg2+(aq) + 2e− → Mg(s) − 2.37 Stronger reducing agent Na+ (aq) + e− → Na(s) − 2.71 Li+ (aq) + e− → Li(s) − 3.04 The arrangement of various electrodes in the increasing order of standard reduction potentials. Potential difference between electrode and electrolyte. = − 0 0 cell Righ left E E E Electrode potential Faraday Laws Faraday 1st Law Amount of chemical reactions which occurs at any electrode during electrolysis by a current is proportional to the quantity of electricity passed through electrolyte → W = zit • Faraday 2nd Law Amount of substance deposited at electrodes during electrolysis is proportional to their chemical equivalents weights → • = = 1 2 3 1 2 3 W W W E E E Quantitative Aspects Nature of Electrode Medium of Electrolyte ElectrochemistryElectrochemistry Electrolytic Cell Galvanic/Voltic Cell CathodeAnode + Vely charged reduction takes place + Vely charged Oxidation takes place Salt Bridge U shaped inverted tube connecting two electrolyte solution 4 4 4 4 4 kc c = ∝ ∝ 2 1- APPLICATION 1 Resistance l a = cell constant l a 1000 × K M 1000 × K N • Conductance [G] = unit: Ohm-1 or Siemens • Specific conductivity (K) = unit: Ohm-1 cm-1 or S cm-1 • Molar conductance (Λm) = unit: Scm-1mol-1 • Equivalent conductance (Λeq) = unit: Cm2 ohm-1 g-e -1 q G n Hydrogen gas at 1 atm Platinum foil Hydrogen io Standard Hydrogen Electrode (SHE) For SHE, E0 cell = 0 Electro chemical phenomenon in which metal oxide of metal forms coating on metyal surface. • Painting, barrier protection, rust solution. n n n n n n n Z On n n n 2 2 2