1. Stoichiometry of Cell Reactions and Free Energy

2. Basic Concepts 1.q = It where: q = charge in Colombs (C) I = current in Amperes (A) t = time in seconds (s)  1C = 1A x 1s and 1A = C/s 2.Faraday’s Law: the mass of a substance formed or consumed is directly related to the charge transferred

3. 3.Faraday = the charge of 1 mol of e - F = 9.65 x 10 4 C/mol 4. and eg.1Calculate the amount of charge which passes through an electrolytic cell with a current of 1.80A for 5.0 min. q= It = 1.80 Cs -1 x 5.0 min x 60 s/1min = 5.4 x 10 2 C

4. eg. 2Calculate the mass of Zn deposited by a current of 2.50 A operating over 30.0 min in an electrolytic cell containing Zn(NO 3 ) 2(aq). Zn 2+ + 2e - ↔Zn I = 2.50 A m =? t = 1800 s M= ? m Zn = n Zn x MZn = n e- x mole ratio x M Zn =

6. Free Energy & Electrochemistry ΔGº = ΔHº - TΔSº and ΔGº = -RTlnK eq and… ΔGº = -nFΔEº cell  RTlnK eq = nFΔEº cell then… R = 8.314 J/molK

7. eg.Calculate ΔGº and K eq for the electrolytic Zn/Al cell, Al│Al 3+ │Zn. an (ox): 3(Zn ↔ Zn 2+ + 2e - ) Eº = -(-0.76)V cat (red): 2(Al 3+ + 3e - ↔ Al) Eº = -1.66V 3 Zn + 2 Al 3+ ↔ 2 Al + 3 Zn 2+ ΔEº cell = -0.90V ΔGº = - nFΔEº cell = - 6mol (9.65 x 10 4 C/mol) (- 0.90V) = + 5.2 x 10 5 CV = + 5.2 x 10 5 J = + 5.2 x 10 2 kJ (beware of sign for ΔGº)