# What happens when two galvanic cells are placed in series

I understand how a single galvanic cell works, and the relation of equilibrium and the Nernst equation. But this appears to contradict the higher voltage in a series configuration because it basically tells you there is a limit of how much excess charges can the plates build up before the reactions halts, So how does placing two cells in series increases the potential difference?

Someone answered about the potential difference being a relative thing and I accept this idea but I don't get how does this apply to this situation.

• Try these 3 things: 1/Imagine the very left electrode is grounded. 2/ Imagine there is inserted the standard H electrode to each of the 2 cells as the reference. 3/ Write down for each of 6 electrodes their electrostatic potential wrt ground and their electrochemical potential. – Poutnik Jul 7 '19 at 6:37

It is very analogical scenario as connecting capacitors or electronic DC sources ( with floating potentials ) in a serie.

With 2 cells in a serie, the same provided charge spends the doubled amount of electrode material. And vice versa for charging.

Even without looking into electrochemistry details, energy conservation law requires doubled voltage for 2 identical cells in a serie.

In fact, such voltage doubling has nothing to do with electrochemistry.

Remember that electrolyte in cells has it electrostatic potential, and that thede potentials differ between cells by the cell voltage.

Potentials in cells, in the electrochemistry context, are floating potentials, related to potential of the standard hydrogen electrode, would be put into the cell.

In context of physics, the same electrode in cells in a serie, including the hydrogen one, has different electrostatic potential wrt (physical) infinity, what is conventional zero potential reference.

Electrochemical potentials of electrodes are electrostatic potentials related not to physical infinity as we are used to, but to (would be there ) the electrostatic potential of the standard hydrogen electrode in the same cell.

If cells are connected to a serie, electrostatic potentials of the same respective electrodes across the serie differ by the multiple of the cell voltage.

• I get your last paragraph but i can't figure out how to apply it in the context of galvanic cells in series i think that there will be a short circuit between the inner plates and the voltage will stay the same between the outer plates – mohamed azaiez Jul 6 '19 at 6:47
• Imagine 2 transformers with floating ends of their secondary circuit. Join 1 end from 1 transformer with 1 end of the other transformer. Is there any short circuit ? Remember,joining cells is not about electrochemistry at all. – Poutnik Jul 6 '19 at 7:10
• I have updated the answer. – Poutnik Jul 6 '19 at 7:52
• Transformer are out of my reach for now but i know capacitors well enough , what is this standard hydrogen electrode ? – mohamed azaiez Jul 6 '19 at 7:57
• Thanks for the effort in your awnser but i didn't really understand this sentence "the same provided charge spends the doubled amount of electrode material.' what do you mean by 'spends' in this context , – mohamed azaiez Jul 6 '19 at 8:00

Voltage and (thermodynamic) electrode potential are slightly different things. Electrode potential refers to the maximum amount of work that can be extracted from a given single cell under very specific conditions and at a given concentration of metal ions.

Now forget about the cells shown in chemistry textbooks. First think of a hydraulic analogy. Think of two identical pumps connected in series in a closed loop, what will happen to the pressure (voltage) in the pipe? The amount of water (=current) entering pump 1 is the same as the amount of water that enters pump 2, however the pressure sensor will show increase in the pressure by a factor of 2.

Basically, voltage adds up in series for two cells.

But this appears to contradict the higher voltage in a series configuration because it basiclly tells you there is a limit of how much excess charges can the plates build up before the reactions halts

This is a misconception. There is no gradual build up of charge.