question_answer 19)

Calculate the standard cell potentials of galvanic cell in which the following reactions take place : (i) 2Cr (s) + 3 Cd2+ (aq) ® 2 Cr3+ (aq) + 3 Cd E0Cr3+ /Cr = ? 0.74 V and E0Cd 2+/Cd = ? 0.40V (ii) Fe2+ (aq) + Ag+ (aq)  Fe3+ (aq) + Ag (s) E0Ag+ /Ag = 0.80 V and E0Fe 3+ /Fe = 0.77V Calculate the and equilibrium constant of the reactions.  

Answer:

(i) (a) Calculation of standard cell potential (i) E0cell = E0c ? E0a = E0Cd2+/Cd ? E0Cr3+ /Cr = ? 0.40 ? (? 0.74) = ? 0.40 + 0.74 = + 0.34 V (b) Calculation of = ? nFE0 cell = ? 6 × 96500 C × 0. 34 V = ? 196860 J = ? 196.86 kJ/mol (c) Calculation of equilibrium constant = ?2.303 RT log Kc log Kc = 34.501 Kc = antilog (34.501) = 3.17 × 1034 (ii) Solve in the same way (a) E0cell = 0.03 V (b) = ? 2.895 kJ mol?1 (c) Kc = 3.2