Question

What would the potential of a standard hydrogen (S.H.E.) electrode be if it was under the following conditions? [H+] = 0.43 M PH2 = 3.9 bar T = 298 K

Answer 1

at standard condition cell reaction when Hydrogen is an electrode is

2H+ (aq) + 2e- -> H2(g)

The potential for a nonstandard cell is: E = E° - (RT/nF) ln Q

where

E° is the standard cell potential = 0.00

R is the gas constant (8.314 J/mol-K)

T = temperature = 298K

n is the number of electrons involved in the reaction = 2

F is Faraday's constant (96485 C/mol)

Q is the reaction quotient

For the cell reaction above, Q = (Pressure H2]) / [H+]²

Pressure of H2 = 3.9 bar convert in to atm = 3.85atm

[H+] = 0.43 M

Q = 3.85 / [0.43]² = 3.85 / 0.1849 = 20.822

put all these values in the given equation

E = 0 - (8.314 x 298 / 2 x 96485) ln(20.822)

E = - (2477.572 / 192970) 3.036

E = -0.04 V