Question

For the following two half-cell reaction Fe3+ + e- --> Fe2+ and I3- + 2e- --> 3 I- determine the spontaneous reaction (balanced). Must give a short reason for choice. Calculate the standard cell potential. Calculate the free energy of the reaction at standard conditions

Answer 1

first find the reduction potentials

Fe+3 + e- ---> Fe+2 Eo = 0.77

I3- + 2e- --> 3I- Eo = 0.53

we know that

the electrode with more reduction potential is cathode

so

iron is cathode

now

cathode : reduction

2Fe+3 + 2e ---> 2Fe+2

anode : oxidation

3I- + 2e- --> I3-

so

the balanced reaction is

3I- + 2Fe+3 ---> I3- + 2Fe+2

now

Eo cell = Eo cathode - Eo anode

Eo cell = 0.77 - 0.53

Eo cell = 0.24 V

now

dGo = - n x F x Eo

here

n =2 as two electrons are transferred

so

dGo = - 2 x 96485 x 0.24

dGo = -46313

dGo = - 46.313 kJ