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Reversible and Irreversible Cells Reversible and Irreversible
cells REVERSIBLE AND IRREVERSIBLE CELLS Daniell cell has the emf
value 1.09 volt. If an opposing emf exactly equal to 1.09 volt
is applied to the cell, the cell reaction, Zn + Cu2+ --> Cu +
Zn2+ stops but if it is increased infinitesimally beyond 1.09
volt, the cell reaction is reversed. Cu + Zn2+ --> Zn + Cu2+
Such a cell is termed a reversible cell. Thus, the following are
the two main conditions of reversibility: (i) The chemical
reaction of the cell stops when an exactly equal opposing emf is
applied. (ii) The chemical reaction of the cell is reversed and
the current flows in opposite direction when the opposing emf is
slightly greater than that of the cell. Any other cell which
does not obey the above two conditions is termed as
irreversible. A cell consisting of zinc and copper electrodes
dipped into the solution of sulphuric acid is irreversible.
Similarly, the cell is also irre