26 No. 6
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Electromotivity to Replace Electromotive Force?
by Vladimir Simeon
As generally known, the so–called electromotive force is an important parameter of the reaction taking place in an electrochemical cell because it is proportional to the reaction gradient of Gibbs energy:
ζ and ν denote the advancement (extent) of the cell reaction and the number of exchanged electrons, respectively. If the leads connecting the electrodes to the measuring instrument are identical in chemical composition, the electromotive force can be defined 1,2 as the zero-current limit of the Galvani potential difference between two electrodes:
The traditional name “electromotive force” (in use since 1827)3 is obviously inconsistent with the definition (2) and the term “force” is potentially misleading. Nevertheless, this name is still widely used and has its place in authoritative international manuals of recommended terminology and symbols, such as IUPAC’s “Green Book”1 and “Compendium”4 or ISO 31,5 not to speak of numerous textbooks. Several alternatives to the name “electromotive force” have been proposed, one of the more recent ones being the four-word phrase zero-current cell potential.6
By inspecting the family of words containing the common fragment “motiv,” it can be seen that one of its members is the word “motivity” (first recorded around 1687)3 meaning “the power of moving or producing motion.”3,7 The word “motivity” may be used to devise a suitable substitute for the name “electromotive force,” viz. ELECTROMOTIVITY.
There are some important advantages of using the term “electromotivity” for E, instead of “electromotive force” or “zero-current cell potential”:
• The meaning of the proposed name, “electromotivity,” is perfectly consistent with the defining equation (2) where the zero-current conditions are additionally stipulated.
• Consisting of one single word, the proposed name is both economical and easy to combine into composite names or phrases (e.g. standard electromotivity, relative standard electromotivity, thermal electromotivity, etc.).
• The equivocal word “potential” (having at least three meanings: potential, potential difference, potential energy) is not used.
Believing that these reasons are sufficient, I am proposing the acceptance of the name “electromotivity” for the physical quantity E, defined by Eq. (2), as a recommended substitute for the traditional name “electromotive force.”
1. I. Mills, T. Cvitaš, K. Homann, N. Kallay, and K. Kuchitsu, Quantities, Units and Symbols in Physical Chemistry, 2nd ed., Blackwell, Oxford 1993, pp. 14, 58–62.
2. D.J.G. Ives and G.J. Janz, Reference Electrodes, Academic Press, New York 1961, pp. 4-8.
3. Merriam-Webster’s Collegiate® Dictionary, 10th ed. (2001).
4. A.D. McNaught and A. Wilkinson, Compendium of Chemical Terminology, 2d ed., Blackwell, Oxford 1997, p. 131.
5. ISO 31-5:1992(E) 5-6.3.
6. P.W. Atkins, Physical Chemistry, 5th ed., Oxford University Press, Oxford 1994, p. 331.
7. H.W. Fowler and F.G. Fowler, The Concise Oxford Dictionary of Current English, 4th ed., Clarendon Press, Oxford 1952, p. 772.
Vladimir Simeon <[email protected]> is professor at the Department of Chemistry, at the Faculty of Science of the University of Zagreb, Croatia.
last modified 10 November 2004.
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