Electrochemistry
Electrochemistry covers galvanic cells, electrode potentials, conductivity and electrolysis. Expect Nernst calculations, cell-symbol interpretation and Faraday problems.
Cells and potentials
For a cell, Ecell = Ecathode - Eanode = Eright - Eleft. A positive Ecell means spontaneous reaction. Delta G0 = -n F E0 and log K = n E0/0.0591 at 298 K. The Nernst equation is E = E0 - (0.0591/n) log Q. Oxidation occurs at the anode; reduction at the cathode. In the Daniell cell, Zn is anode and Cu is cathode.
Conductance and electrolysis
Molar conductivity Lambda_m = kappa/c, with c in mol/cm3 when kappa is in S/cm. Kohlrausch's law: Lambda_m infinity = v+ lambda+ + v- lambda-. Degree of dissociation alpha = Lambda_m/Lambda_m infinity. Charge Q = I t; moles deposited = Q/(nF), with F = 96500 C/mol.
Worked example
For Zn|Zn2+||Cu2+|Cu, E0 = 1.10 V. The reaction is Zn + Cu2+ -> Zn2+ + Cu, so Q = [Zn2+]/[Cu2+]. If [Zn2+] = 0.10 M and [Cu2+] = 1.0 M, n = 2: E = 1.10 - (0.0591/2) log(0.10) = 1.10 + 0.0296 = 1.13 V. The cell voltage rises because the product concentration is lowered relative to standard conditions.
Traps
Reversing Q, subtracting the anode potential the wrong way, and using n = 1 for a two-electron cell are frequent errors.