Question

Using the following standard reduction potentials,

Fe³⁺(aq) + e^- --> Fe²⁺ (aq) E = + 0.77 V

Ni²⁺ (aq) + 2e^- (aq) --> Ni(s) E = - 0.26 V

Calculate the standard cell potential for the galvanic cell reaction given below and determine weather or not if the reaction is spontaneous under standard conditions.

Ni²⁺ (aq) + 2 Fe²⁺ (aq) --> 2 Fe³⁺ (aq) + Ni(s)  

SHOW ALL WORK

Answer 1

Given standard reduction potentials

Fe3+(aq) + e- --> Fe2+ (aq) E = + 0.77 V

Ni2+ (aq) + 2e- (aq) --> Ni(s) E = - 0.26 V

But here Fe2+ to Fe3+(aq) half cell is on the left so this is the oxidation half cell so the half cell reaction is reversed.

Fe2+ (aq) ------> Fe3+ (aq) + e- E° = -0.77 V ------- (i)

Ni2+ (aq) + 2e- (aq) --> Ni(s) E = - 0.26 V -------(ii)

To balance the electrons, these must be combined with 2 × (i) and (ii):

Ni2+ (aq) + 2 Fe2+ (aq) --> 2 Fe3+ (aq) + Ni(s)  

E° = [Eox+Ered]=[(-0.77) + (-0.26)} V = -1.03 V

Now we know the relation between deltaG and E° is deltaG=-nFE°

where n=number electrons=2, F=faraday=96458 C

deltaG=-(2)x(96458 C)(-1.03 V)=198703 J

deltaG=198.703 kJ.

If deltaG>0, the process is non spontaneous.