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Which Eo Is It? The Story of a Student Discovery

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Ron C. Cooke and Grover C. Willis

California State University-Chico, Chico, CA 95929-0210

J. Chem. Educ., 1996, 73 (5), p 450

DOI: 10.1021/ed073p450

Publication Date (Web): May 1, 1996

Section:

History, Education, and Documentation

Abstract

A homework problem called for the computation of the E^o for the reaction 2Cu+ --> Cu+2 + Cu. Two students independently worked on this problem and calculated answers of +0.359 V and +0.181 V respectively, using E^o for the half reactions from a table in the book.

When they compared answers, they were confused--both were sure they did the problem correctly. The answer in the back of the book (+0.359 V) did not clarify the situation--one student still did not understand what he did wrong and wondered if the E^o for the half reactions were incorrect in his book.

We suggested that it might be helpful for them to draw the formal representations for the electrochemical cells in question and then compute the delta G using each of their E^o values.

The puzzle was solved when the students saw that although each had drawn a different cell, the delta G was the same for both cells and realized that the delta G was independent of pathway, the value of E^o and n in delta G = -nFE^o may vary depending on the cell construction.