calculate the pH of ph2 /H+//h+/ph2 .ecell =0.2364
Answers
Answer:
How does pH affect the Nernst equation?
Chemistry Calculating Energy in Electrochemical Processes
1 Answer
Ernest Z. · Media Owl
Sep 25, 2014
pH doesn't affect the Nernst equation.
But the Nernst equation predicts the cell potential of reactions that depend on pH.
If H⁺ is involved in the cell reaction, then the value of
E
will depend on the pH.
For the half-reaction, 2H⁺ + 2e⁻ → H₂,
E
∘
= 0
According to the Nernst equation,
E
H⁺/H₂
=
E
∘
−
R
T
z
F
ln
Q
=
−
R
T
z
F
ln
(
P
H₂
[H⁺]
2
)
If
P
H₂
= 1 atm and
T
= 25 °C,
E
H⁺/H₂
=
−
R
T
z
F
ln
(
P
H₂
[H⁺]
2
)
=
−
8.314 J⋅K
−
1
×
298.15 K
2 × 96 485 J⋅V
−
1
×
ln
(
1
[H⁺]
2
)
= 0.012 85 V × 2ln[H⁺] = 0.02569 V × 2.303log [H⁺]#
E
H⁺/H₂
=
-0.059 16 V × pH
EXAMPLE
Calculate the cell potential for the following cell as a function of pH.
Cu²⁺(1 mol/L) + H₂(1 atm) → Cu(s) + 2H⁺(aq)
Solution
Cu²⁺ + 2e⁻ → Cu;
E
∘
= +0.34 V
H₂ → 2H⁺ + 2e⁻;
E
∘
= 0
Cu²⁺ + H₂ → Cu + 2H⁺;
E
∘
= +0.34 V
E
∘
Cu²⁺/Cu
= E^° - (RT)/(zF)ln(1/[Cu²⁺]) = E^° + 0 = +0.34 V
E
H₂/H⁺
=
−
E
H⁺/H₂
= 0.059 16 V × pH
E
cell
= (0.034 + 0.059 16 × pH) V