Question

The `E^(o)` values of the following reduction reactions are given
`Fe_((aq))^(3+)+etoFe_((aq))^(2+),E^(o)=0.771V`
`Fe_((aq))^(2+)to2etoFe_((s)),E^(o)=-0.447V`
What will be the free energy change for the reaction
`Fe_((aq))^(3+)+3e^(-)toFe_((s))" "(1F=96485C" mol"^(-1))`
A. `+18.51kJ" "mol^(-1)`
B. `+11.87kJ" "mol^(-1)`
C. `-8.10kJ" "mol^(-1)`
D. `-10.41kJ" "mol^(-1)`

Answer 1

Correct Answer - B
`DeltaG^(o)=-nFE_(cell)^(o)`
`Fe_((aq))^(3+)+e^(-)toFe_((aq))^(2+),DeltaG_(1)^(o)=-Fxx0.771`
`Fe_((aq))^(2+)+2e^(-)toFe_((s)),DeltaG_(2)^(o)=-2xxFxx(-0.447)`
`=0.894F`
`Fe_((aq))^(3+)+3e^(-)toFe_((s)),DeltaG_(3)^(o)=?`
`DeltaG_(3)^(o)=DeltaG_(1)^(o)+DeltaG_(2)^(o)`
`DeltaG_(3)^(o)=-0.771F+0.894F`
`DeltaG_(3)^(o)=0.123F=0.123xx96485`
`DeltaG_(3)^(o)=11867.6J" "mol^(-1)` or `11.87kJ" "mol^(-1)`.