If standard reduction potential (E^0) of ( Al ^ +3 _ (aq) | Al _ (s) ), ( Fe ^ +2 _ (aq) | Fe _ (s) ), ( Cu ^ +2 _ (aq) | Cu _ (s) ) and ( Ag ^ +1 _ (aq) | Ag _ (s) ) are -1 66 V, -0 44 V, +0 34 V and +0 79 V respectively. Which of the following reaction is non spontaneous ?
A. 2 Ag _ (s) + Fe ^ +2 _ (aq) 2 Ag ^ +1 _ (aq) + Fe _ (s)
For a reaction to be non-spontaneous, the standard cell potential E^ 0 _ cell must be negative, where E^ 0 _ cell = E^ 0 _ cathode - E^ 0 _ anode . For the reaction 2 Ag _ (s) + Fe ^ +2 _ (aq) 2 Ag ^ +1 _ (aq) + Fe _ (s) : Ag undergoes oxidation (anode) and Fe ^ +2 undergoes reduction (cathode). E^ 0 _ cell = E^ 0 _ Fe ^ +2 / Fe - E^ 0 _ Ag ^ + / Ag E^ 0 _ cell = -0.44 - 0.79 = -1.23 V Since E^ 0 _ cell For the other reactions, E^ 0 _ cell is positive, making them spontaneous: 2 Al _ (s) + 3 Cu ^ +2 _ (aq) 2 Al ^ +3 _ (aq) + 3 Cu _ (s) E^ 0 _ cell = 0.34 - (-1.66) = +2.00 V Fe _ (s) + Cu ^ +2 _ (aq) Fe ^ +2 _ (aq) + Cu _ (s) E^ 0 _ cell = 0.34 - (-0.44) = +0.78 V 2 Al _ (s) + 3 Fe ^ +2 _ (aq) 2 Al ^ +3 _ (aq) + 3 Fe _ (s) E^ 0 _ cell = -0.44 - (-1.66) = +1.22 V Answer: 2 Ag _ (s) + Fe ^ +2 _ (aq) 2 Ag ^ +1 _ (aq) + Fe _ (s)
Related: Chemistry — Electrochemistry · All PYQ Banks