I see the questions of why a galvanic cell needs a salt bridge and why a electrolytic cell doesn't need a salt bridge being answered separately but I still can't grasp why you are not allowed to mix or interchange the reasons of the two. Can someone explain why both cells are set up in that way and provide a comparison?

From what I've read, it has to do with some of the following differences but I can't seem to put it together into a common picture.

  1. A galvanic cell needs to prevent electrolyte mixing in order to produce current. Of course electrolytes need to be connected in order to maintain neutrality. But instead of a direct connection such as using the same electrolyte for both electrodes, the electrolytes for the anode and cathode are separated but connected by a salt bridge in order to maintain this neutrality but prevent the electrolyte mixing by having ions pass at a rate not too high. Could someone explain again what electrolyte mixing has to do with the current? Meanwhile since in an electrolytic cell, the chemical reactions are what is being produced the electrolytes can be mixed.
  2. The electron supply in both are different. For a galvanic cell, it is supplied by the species getting oxidized. For an electrolytic cell, the external battery supplies the electrons.
  3. I should also reiterate here how galvanic cells have spontaneous chemical reactions and do not need the external voltage supply while electrolytic cells have nonspontaneous chemical reactions and need the external voltage supply.
  4. For a galvanic cell, the anode is negative while the cathode is positive. For an electrolytic cell, the anode is positive while the cathode is negative. However, it should be noted that by definition an anode always has oxidation while a cathode always has reduction.
  5. It should be noted that the flow of electrons is the same when based on the charge of the electrode. Electrons always move from the negative electrode to the positive electrode. For galvanic cell it is anode to cathode while for an electrolytic cell it is cathode to anode.

It's not like I can't understand the two concepts of the galvanic and electrolytic cells separately. But I want to be able to fully understand the comparison and contrast on why you can't just interchange the two and how their many opposites and differences have something to do with that.

  • 1
    $\begingroup$ Look at my drawing of a Daniell cell: chemistry.stackexchange.com/a/118744/79678. If you get rid of the salt bridge and just use one beaker with a mixture of the two solutions, then zinc metal will spontaneously be oxidized by the copper ions, thereby wasting the available free energy as heat, instead of getting electrical energy via the external electrode pathway. This is trivially simple to demonstrate: place a zinc metal strip in a copper sulfate solution. Zinc gets oxidized and copper plates out, usually as a poorly adherent coating. $\endgroup$
    – Ed V
    May 19, 2021 at 23:38
  • 2
    $\begingroup$ Think of a typical battery cell. If you discharge then it is a galvanic cell, if you are charging it then it is electrolytic cell. Thus your supposition isn't true. $\endgroup$
    – MaxW
    May 20, 2021 at 8:50
  • 2
    $\begingroup$ Salt bridges or equivalents keep cells from more or less fast reaching the chemical equilibrium. While electrolysis can be done any time, even for systems in equilibrium, systems in equilibrium do not provide electromotoric power, their voltage is zero. $\endgroup$
    – Poutnik
    May 20, 2021 at 9:47


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