Question

Calculate δg∘rxn and e∘cell for a redox reaction with n = 3 that has an equilibrium constant of k = 4.4×10−2. you may want to reference (pages 861 - 865) section 19.5 while completing this problem.'

Answer 1

a) First, to get ΔG°rxn we have to use this formula when:

ΔG° = - RT ㏑ K 

when ΔG° is Gibbs free energy 

and R is the constant = 8.314 J/mol K

and T is the temperature in Kelvin = 25 °C+ 273 =  298 K 

and when K = 4.4 x 10^-2

so, by substitution:

ΔG°= - 8.314 * 298 *㏑(4.4 x 10^-2)

      = -7739 J  = -7.7 KJ


b) then, to get E° cell for a redox reaction we have to use this formula:

ΔE° Cell = (RT / nF) ㏑K

when R is a constant = 8.314 J/molK

and T is the temperature in Kelvin = 25°C + 273 = 298 K

and n = no.of moles of e- from the balanced redox reaction= 3

and F is Faraday constant = 96485 C/mol

and K = 4.4 x 10^-2

so, by substitution:

∴ ΔE° cell = (8.314 * 298 / 3* 96485) *㏑(4.4 x 10^-2)

              = - 2.7 x 10^-2 V