19-7. Calculate the theoretical potential of the following cells. Indicate whether the reaction will proceed spon- taneously in the direction considered (oxidation on the left, reduction on the right) or whether an exter- nal voltage source is needed to force this reaction to occur. (a) Pb Pb (0.120 M)||Ca (0.0500)|Cd (b) Zn/Zn (0.0420 M)||TI (9.06 X 10M), TI* (0.0400 M)|P (c) Pt. H,(757 torr) |HC(2.00 x 10-* M)|| Ni (0.0400 M)|Ni (d) Pb Pbl,(sat'd), I (0.0220 M)||Hg (2.60 X 10M) Hg (e) Pt. H,(1.00 atm)|NH,(0.400 M), NH," (0.200 M)||SHE (f) PrTiO2 (0.0450 M), T* (0.00320 M). H(3.00 X 10M)||VO2+ (0.1600 M), V3(0.0800 M), H* (0.0100 M)|Pt