Cell Electrode Potentials
- The Electromotive Force (EMF) equation, also known as the Cell Electrode Potential equation, consists of two known constants, R and F, and five experimental terms.
- Given all but one of the experimental terms, this tool solves for the missing one.
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- The Nernst Equation given above relates the electromotive force of an electrochemical half- or full-cell reaction to the Standard Electrode Potential, temperature, activities of reactant and products, and number of electron transferred during the net redox (reduction and oxidation) reaction (Chem.LibreTexts.org, 2015; Wikipedia, 2017) where
R is the gas constant defined as 8.3144598(48) J·K-1·mol-1.
F is the Faraday constant defined as 96485.33289(59) C·mol-1.
E is the electromotive force in Voltz (V).
E° is the standard electrode potential in Voltz (V).
T is the temperature in the Kelvin scale.
n is the number of electrons transferred during the net redox reaction.
Qeq is a reaction quotient or ratio of reactants and product activities (often approximated by concentrations). Important Notes
If T is in Celsius, Fahrenheit, Rankine, or other units, it must be converted to kelvins. We have developed a Temperature Converter tool that simplifies all these conversions.Units conversions
When changing units, you may want to follow NIST 2006 guidelines for expressing results to a given number of significant digits:- If the first significant digit of the converted value is greater than or equal to the first significant digit of the original value, round the converted value to the same number of significant digits as there are in the original value.
- If the first significant digit of the converted value is smaller than the first significant digit of the original value, round to one more significant digit.
- Lab techs as well as chemistry teachers and their students.
- Calculate the potential for the following cell at room temperature:
Zn|Zn2+ (0.1 M) || Cu2+ (0.2 M) | Cu
where at 25 °C
Cu2+ + 2e- → Cu ; E° = 0.337 V
Zn2+ + 2e- → Zn ; E° = -0.763 V
- How would you classify the above cell?
- galvanic
- electrolytic
- voltaic
- Daniell
- How would you classify the above cell?
- primary
- secondary
- reserve
- fuel
- Calculate the EMF of the above cell if one of the electrode solution is ten-fold diluted.
- Calculate the EMF of the above cell if both electrode solutions are ten-fold diluted.
- Chem.LibreTexts.org (2015). Cell EMF.
- NIST (2006). The International System of Units (SI) - Conversion Factors for General Use. Nist Special Publication 1038.
- Wikipedia (2017). Nernst Equation.
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