Answer Happy

Example: Which of the following reactions is spontaneous based on the standard reduction potentials? Note that Reaction 2 is just the reverse of Reaction 1. Reaction 1. Cu(s) + 2 Ag (aq) - Cu?" (aq) + 2 Ag(s) Reaction 2. 2 Ag(s) + Cu?" (aq) - 2 Ag (aq) + Cu(s) -
Answer: From the table of standard reducton potentials, we find that the standard reduction potentials are: Cu?" (aq) + 2e - Cu(s), E = +0.34 V (two significant digits) Ag (aq) + e - Ag(s), E° = +0.80 (two significant digits) To get Reaction 1, we use combine 2 x (the silver half reaction) with the reverse of copper half reaction). In other words, • is reduced and is oxidized. Note that the silver half reaction has to happen twice every time the copper half reaction occurs to balance electrons lost and electrons gained. Therefore: Eredº = V (two significant digits); we do not multiply this by 2 even the coefficients are multiplied by 2 because the potentials are intensive properties. Ex = V (two significant digits); we change the algebraic sign since we reversed the half reaction The standard cell potential for Reaction 1 is the sum of Ered and Eox": Ecellº for Reaction 1 = V (two significant digits), Since Reaction 2 is just the reverse of Reaction 1, Ecel for Reaction 2 to be V (two significant digits).