# Does standard electrode potential depend upon temperature?

Does standard reduction potential depend on temperature?

I am confused because my institute gives the definition for standard reduction potential as the potential that is measured at standard state which defines as measured in atmospheric pressure at $$\pu{298 K}$$, and when the concentration of all the substances is unity. But as far as my understanding goes standard states can be defined at any temperature and not just $$\pu{298 K}$$.
Also, as its directly related to $$\Delta G^\circ = -nFE_\mathrm{cell} = \Delta H^\circ - T\Delta S^\circ$$, this points toward it being dependent on temperature. Also, when someone says standard state, does that put restriction on temperature being $$\pu{298 K}$$??

• Yes, see the Nernst Equation. – MaxW Jun 18 '20 at 19:27
• @MaxW Thank You, but I still don't get it, how does nerst equation help ?? Like all it does is relate electrode potential to standard electrode potential , it says that the electrode potential will depend on temperature, but nothing about the standard electrode potential – Manish Mittal Jun 18 '20 at 20:40
• I think I disagree with @MaxW here, but it's really over semantics, not over the substance of his point. The standard potential is standard. If you have a non-standard state, then you have a different value. In other words, the standard value is constant, but the actual electrode potential definitely depends on temperature. – Zhe Jun 18 '20 at 20:40
• @Zhe Does the standard state mean it's only at 298 K ?? – Manish Mittal Jun 18 '20 at 20:41
• The standard state is 298 K. I would not expect the potential to be the same if you change the temperature... – Zhe Jun 18 '20 at 20:57

## 1 Answer

Yes, the standard reduction potential does depend on temperature. The definition of the standard reduction potential is stated in Ref.1 as:

A standard electrode potential $$E^\circ$$ is defines as the potential (in Volts, $$\pu{V}$$) of a half-reaction relative to a reference electrode at a specific temperature, all chemicals being at their standard states at unit activity. These states may be arbitrarily defined as pure crystalline solids, pure liquids, ideal gases at one atmosphere fugacity ($$\pu{101325 \times 10^{5} Pa}$$), and ideal solutes at unit molality. The most common temperature for the tabulation of standard electrode potentials, as for their thermodynamic data, is $$\pu{25 ^\circ C}$$ ($$\pu{298.15 K}$$).

Accordingly, tabulated data is chosen to be at $$\pu{298.15 K}$$ for the convenience. This is also beneficial that the most common reference electrode is the Standard Hydrogen Electrode (SHE) for the solvent water:

$$\ce{2H+_{(aq)} + 2e- <=> H2_{(g)}} \tag1$$

$$E^\circ_{(\ce{H+/H2})}$$ for the above half-reaction is been assigned as zero volts at all temperatures. Extended work over $$\pu{298.15 K}$$ by De Béthune and coworkers shown that the temperature dependence of $$E^\circ$$ is approximately linear between $$\pu{273.15 K}$$ and $$\pu{373.15 K}$$ according to the following equation (Ref.2-Ref.4):

$$E_T = E^\circ_{298} + (T - 298.15)\left(\frac{dE^\circ}{dT}\right)_{298} \tag2$$

References:

1. Steven G. Bratsch, “Standard Electrode Potentials and Temperature Coefficients in Water at $$\pu{298.15 K}$$,” Journal of Physical and Chemical Reference Data 1989, 18(1), 1-21 (https://doi.org/10.1063/1.555839).
2. A. J. De Béthune, T. S. Licht, N. Swendeman, “The Temperature Coefficients of Electrode Potentials: The Isothermal and Thermal Coefficients—The Standard Ionic Entropy of Electrochemical Transport of the Hydrogen Ion,” Journal of The Electrochemical Society 1959, 106(7), 616 (doi:10.1149/1.2427448).
3. G. R. Salvi, A. J. De Béthune, “The Temperature Coefficients of Electrode Potentials: II. The Second Isothermal Temperature Coefficient,” Journal of The Electrochemical Society 1961, 108(7), 672 (doi: 10.1149/1.2428187).
4. André Jacques De Béthune, Nancy A. Swendeman Loud, In Standard Aqueous Electrode Potentials and Temperature Coefficients at $$\pu{25 ^\circ C}$$; C. A. Hampel: Skokie, ILL, 1964.