My chemistry textbook says daniel cells are reversible, but not rechargeable. Why is it that all reversible cells are not rechargeable? Are all rechargeable cells reversible? why/why not?
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1$\begingroup$ Good question. I think the reason is essentially degree rather than kind: rechargeable batteries are designed to be discharged and recharged many times, with minimal deterioration in performance. But non-rechargeable cells, such as the Daniell cell, can be reversed but not brought back to nearly original state. $\endgroup$– Ed VCommented Dec 11, 2021 at 15:01
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$\begingroup$ when I researched a bit more on the internet, I found it is because when Daniel cell is allowed to recharge, reduction of zinc ions to zinc does not take place in the anodic compartment, but evolution of hydrogen takes place. But where did the hydrogen come from? $\endgroup$– Aben PhilipCommented Dec 11, 2021 at 15:37
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1$\begingroup$ @AbenPhilip Water contains hydrogen. $\endgroup$– PoutnikCommented Dec 11, 2021 at 16:06
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1$\begingroup$ Just as Poutnik said. Also, the cell is Daniell, not daniel. $\endgroup$– Ed VCommented Dec 11, 2021 at 16:13
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1$\begingroup$ Moreover reversible has subtle meaning. Often, although not in chemistry, reversible and rechargeable are used as synonyms. $\endgroup$– AlchimistaCommented Dec 11, 2021 at 16:22
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1 Answer
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Per Wikipedia on Electrolytic Cells, to quote:
Galvanic cells compared with electrolytic cells In an electrolytic cell a current is passed through the cell by an external voltage, causing an otherwise nonspontaneous chemical reaction to proceed. In a galvanic cell the progress of a spontaneous chemical reaction causes an electric current to flow. An equilibrium electrochemical cell is at the state between an electrolytic cell and a galvanic cell. The tendency of a spontaneous reaction to push a current through the external circuit is exactly balanced by an external voltage that is called a counter electromotive force or counter e.m.f. so that no current flows. If this counter voltage is increased the cell becomes an electrolytic cell and if it is decreased the cell becomes a galvanic cell.[1]
I do also, operationally, agree with Aben Philip comments, where apparently, attempting to recharge (aka, chemically reverse) a galvanic cell, may undesirably further introduce hydrogen gas. The problematic $\ce{H2}$ gas evolution can result in bursting and the usual safety concerns working with hydrogen (as in an explosion hazard).
More technically from a electrochemistry perspective, per another source, rechargeable batteries are again distinctly claimed again to an "Electrolytic Cell", characterized as having non-spontaneous oxidation-reduction reaction versus spontaneous for a galvanic cell. But further, in addition, they may also have a semipermeable membrane governing the flow of ions, which are not found in a galvanic cell.
I hope this helps.
