REACTION 1: When I buy a new unconnected alkaline cell, has a chemical reaction already occurred on anode end which releases electrons on anode end?

REACTION 2: Also, in the same new unconnected state of the battery, has a chemical reaction occurred at cathode end that captures electrons from cathode end?

After thinking this through I feel that while REACTION 1 happens in a new unconnected battery, the other REACTION 2 does not occur since there are no free electrons to be captured. If REACTION 2 also did occur in a unconnected new battery then the electrolyte would get all consumed and battery would die pretty soon when connected to an external circuit.


1 Answer 1


Both reactions have taken place, but involving only an extremely limited number of electrons. At the cathode electrons have been captured from the cathode assembly, including the metal terminal. But relatively few electrons have been captured, and, indeed, relatively few have been released at the anode.

The reason why only relatively few (relative, that is, to the total number of free electrons in the anode and cathode assemblies) are involved is that those on the anode set up an electric field that opposes more electrons arriving and shuts down the reaction. Similarly the positive charge on the cathode assembly opposes more electrons being taken from the cathode assembly and shuts down the cathode reaction.

As you know, all this changes when you provide an external conducting path between cathode and anode: electrons can now escape from the anode assembly and travel through the conducting path to the cathode. So now the reaction at the anode can proceed and electrons are supplied to the cathode so the reaction at that electrode can proceed as well.

  • $\begingroup$ But on anode end there are no free electrons, so how come electrons can be captured in reducing the cathode material? Free electrons would only be available on cathode side when they flow from anode to cathode through a connected external circuit. $\endgroup$
    – Sunil
    Feb 2, 2021 at 12:45
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    $\begingroup$ Electrons are liberated at the anode within the cell and deposited on the anode assembly. Electrons are taken from the cathode assembly to take part in the reaction at the cathode. $\endgroup$ Feb 2, 2021 at 12:52
  • $\begingroup$ I read somewhere that in an alkaline battery, electrons cannot flow from anode to cathode due to a special material surrounding the electrolyte on anode end that allows ions to pass through but not electrons from anode. I was viewing a video on YouTube which is as at this link youtu.be/PXNKkcB0pI4 $\endgroup$
    – Sunil
    Feb 2, 2021 at 13:06
  • $\begingroup$ That's right; it's ions that travel within the electrolyte. [If I remember rightly, the literal meaning on 'ion' is traveller]. $\endgroup$ Feb 2, 2021 at 13:08
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    $\begingroup$ "so then where is cathode getting 2 electrons for the reaction on its end?" From the electrode assembly itself! That's why the electrode assembly gets a positive charge! But this very positive charge, when it gets large enough (which is in a small fraction of a second) stops more electrons leaving the electrode assembly to take part in the reaction. So the reaction stops. $\endgroup$ Feb 2, 2021 at 15:10

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