Standard Electrode Potentials
- The standard electrode potential equation consists of two known constants, R and F, and four experimental terms.
- Given all but one of the experimental terms, this tool solves for the missing one.
- To use the tool, one of its form fields must be left empty.
- To empty a field, just double click it.
- If no field is left empty, the tool will randomly empty one and recompute its value based on the values of the other fields.
- At equilibrium the electromotive force or net potential of a fuel cell is zero, and thus the standard electrode potential, E°, can be computed from the Nernst Equation given above 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 standard electrode potential in Voltz (V).
T is the temperature in the Kelvin scale.
n is the number of electrons or ion valence.
Keq is a reaction equilibrium constant.
- E° is also called the reversal potential or Membrane Potential in the case of biological membranes, and the equilibrium potential if it is a single ion system (Physiologyweb.com, 2005a; 2005b; 2005c; Physiology.Arizona.edu, 2006; Wright, 2004).
- The Suggested Exercises section lists some relevant problems adapted from the Web (Chem.LibreTexts.org, 2015; Science.UWaterloo.ca, 2007).
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.
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.
A piece of iron is placed in a 1 M Zn2+ solution at 25 °C and the following reaction takes place:
Fe + Zn2+ ⇄ Zn + Fe2+ ; E° = -0.353 V
- Calculate the reaction equilibrium constant.
- What is the equilibrium concentration of Fe2+?
Consider the following reactions at 77 °F:
AgCl + e- ⇄ Ag + Cl- ; E° = 0.2223 V
Ag+ + e- ⇄ Ag ; E° = 0.799 V
- Express the net reaction.
- Calculate the solubility product for the reaction between the silver and chloride ions.
- Calculate the silver and chloride ion equilibrium concentrations.
- Calculate the potential for the following cell at room temperature:
Zn|Zn2+ (1.0 M) || Cu2+ (1.0 M) | Cu
where at 25 °C
Cu2+ + 2e- → Cu ; E° = 0.337 V
Zn2+ + 2e- → Zn ; E° = -0.763 V
- Compare and contrast the following cell types:
- Compare and contrast the following cell categories:
- Chem.LibreTexts.org (2015). Cell EMF.
- NIST (2006). The International System of Units (SI) - Conversion Factors for General Use. Nist Special Publication 1038.
- Physiology.Arizona.edu (2006). The Nernst/Goldman Equation Simulator.
- Physiologyweb.com (2005a). Nernst Potential Calculator.
- Physiologyweb.com (2005b). Electrochemical Driving Force Calculator.
- Physiologyweb.com (2005c). Goldman-Hodgkin-Katz Equation Calculator.
- Science.UWaterloo.ca (2007). Nernst Equation.
- Wright, S. H. (2004). Generation of resting membrane potential.
Contact us for any suggestion or question regarding this tool.