Question

Calculate the standard free energy change, ΔG°, for the following redox reaction:2Fe2+ (aq) + H2O2 (aq) → 2Fe3+ (aq) + 2OH- (aq)Given the following half-reactions and their respective standard reduction potentials:Fe3+ (aq) + e- -> Fe2+ (aq) E° = +0.77 VH2O2 (aq) + 2H+ (aq) + 2e- ⟶ 2H2O (l) E° = +1.78 V

Answer 1

To calculate the standard free energy change  G  for the redox reaction, we first need to determine the overall cell potential  E  and then use the equation:G = -nFEwhere n is the number of moles of electrons transferred and F is the Faraday constant  96,485 C/mol .First, we need to balance the half-reactions:1. Fe3+  aq  + e- -> Fe2+  aq  E = +0.77 V2. H2O2  aq  + 2H+  aq  + 2e-  2H2O  l  E = +1.78 VTo balance the electrons, we need to multiply the first half-reaction by 2:1. 2Fe3+  aq  + 2e- -> 2Fe2+  aq  E = +0.77 VNow, we need to reverse the first half-reaction to match the given redox reaction:1. 2Fe2+  aq  -> 2Fe3+  aq  + 2e- E = -0.77 VNext, we add the two half-reactions:2Fe2+  aq  + H2O2  aq  + 2H+  aq  + 2e- -> 2Fe3+  aq  + 2e- + 2H2O  l Cancel out the 2e- on both sides:2Fe2+  aq  + H2O2  aq  + 2H+  aq  -> 2Fe3+  aq  + 2H2O  l Now, we need to balance the H+ and OH- ions by adding 2OH- to both sides:2Fe2+  aq  + H2O2  aq  + 2H+  aq  + 2OH- -> 2Fe3+  aq  + 2H2O  l  + 2OH-This simplifies to the given redox reaction:2Fe2+  aq  + H2O2  aq  -> 2Fe3+  aq  + 2OH-  aq Now we can calculate the overall cell potential  E  by adding the potentials of the two half-reactions:E = -0.77 V + 1.78 V = 1.01 VSince 2 moles of electrons are transferred in the balanced redox reaction, n = 2. Now we can calculate the standard free energy change  G :G = -nFEG = - 2 mol  96,485 C/mol  1.01 V G = -194,658.7 J/molThe standard free energy change  G  for the given redox reaction is -194,658.7 J/mol.