Question

The standard potentials for the reduction of nicotinamide adenine dinucleotide (NAD+) and oxaloacetate (reactants in the multistep metabolism of glucose) are as follows: E° = –0.330 V E° = –0.166 V n=2 Calculate the equilibrium constant at 298.15 K for the reaction.

Answer 1

Since reduction potential of oxaloacetate is greater than NAD+ for the given reaction

reducing agent: NAD+

Oxidising agent: Oxaloacetate

E⁰_cell = reduction potential of reduction half - reduction potential of oxidation half

E⁰_cell = E⁰ of oxaloacetate - E⁰ of NAD+

E⁰_cell = -0.166 - (-0.330) V = +0.164 V

We know the relation between equilibrium const. ​G⁰ and E⁰_cell

​G⁰ = -RTlnK = -2.303 x RT log K

and ​G⁰ = -nF​E⁰_cell

From above two equations

2.303 x RT x logK = nF​E⁰_cell

or logK = nFE⁰_cell/ (2.303xRT)

substituting the values logK = 2x 96485.33 x 0.164 / (2.303 x 8.314 x 298.15)

log k = 5.54

K = 3.46 x 10⁵