Question

Calculate the following for the reaction; O2(g) + 4H+(aq) + 4Fe2+(aq) -> 2H2O(l) + 4 Fe3+(aq) (a) ΔGo at 25oC (b) ΔG at 25oC when [Fe2+] = [Fe3+] = 0.200 M, Po2 = 0.800 atm, and the pH = 2.56

Answer 1

ans)

from above data that

For part a, first figure out the # of electrons transferred = 4electrons

Then calculate ΔE^o at 25C (using a redox values) =Ecathode=E anode = 1.23V -0.77 V= 0.46V

Then use the following equation to calculateΔG^o:

ΔG^o = -nFΔE^o = (4 moles ofelectrons)(96485 C mol^-1 )(0.46V)

ΔG^o = - 177532 J = 178 KJ

For Part b use the equation:

calculate [H+] = 10^-pH = 10^-2.56 = 0.00275M

ΔG = ΔG^o + RTInQ, where Q is the reactionquotient
ΔG= -178KJ + (8.314J/mol K)(298 K)In (0.20)^4/(0.20)^4 (0.00275)^4(0.800 atm)

ΔG= -178 KJ + 58.99 KJ = -119.01 KJ