Disclaimer... I have not been involved in electrochemical measurements for
at least 10 years, so I don't know if the terminology used today is
beginning to change. It has not changed in current chemistry textbooks.
In physics it had been common to distinguish between the voltage that would
be measured at the terminals of a battery if the measurement could be made
electrostatically verses that made at the terminals if current is drawn.
When I went to college the electrostatic measurement would be the "emf" and
the voltage under load would be the "terminal potential difference."
Perhaps many physicists have decided to abandon this wording, but the last I
knew, chemists have not abandoned this wording. I think the words used by
electrochemists still involve the idea that a specific chemical reaction has
an associated emf. Measurement of this emf is not necessarily easy and used
to involve a null measurement using a potentiometer and sensitive
galvanometer. Chemical concentrations i.e. chemical activities are also
important and sometimes measurements have to be extrapolated to infinite
dilution. Today "voltmeters" that draw picoamps or even femtoamps have
changed the technology chemists use to make these electrochemical
measurements, but it seems to me that the terminology has not changed.
Recent physical chemistry texts, including the one I use for my class,
heavily make use of emf terminology.
This doesn't necessarily mean we can't change, but we should be aware that
physical chemists use emf quite a bit. Physics students take chemistry, and
chemistry students take physics, and sometimes people end up being both
chemists and physicists. We ought to take a broad picture when we begin
trying to define what terms mean, and which terms should be discarded, etc.
Michael D. Edmiston, Ph.D. Phone/voice-mail: 419-358-3270
Professor of Chemistry & Physics FAX: 419-358-3323
Chairman, Science Department E-Mail edmiston@bluffton.edu
Bluffton College
280 West College Avenue
Bluffton, OH 45817