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I was looking through chemistry textbooks to find out how to determine how much current a galvanic cell should generate and what affects that current value. However, I did not find anything: textbooks just talk about the EMF of a cell.

I wanted to know what determines how much current a cell generates. Certainly, the amount of electrons produced externally contributes to the current produced by the cell. However, what about internally? Batteries have internal resistance. Is that true of cells too (it should be because batteries are made up of many cells)? What determines amount of internal resistance: does the type of electrolyte(s) affect it. If a cell uses a weak electrolyte (like acetic or carbonic acid) will it cause more internal resistance then if something like sulfuric acid (strong electrolyte) is used?

What if a cell used weak electrolyte as the cathode electrolyte and the strong electrolyte was the anode electrolyte, will that cause more internal resistance due to there being less ions in the cathode compartment as not all of the electrolyte has been dissociated into ions (thus, the cathode cation cannot be reduced)?

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Although voltage can be calculated from the electromotive series, maximum current is harder to predict due to a number of factors, some of which you've mentioned.

  1. Electrolyte conductivity, which varies with components, concentration, temperature, etc. As you state, weak electrolytes are less conductive. Resistance of a composite electrolyte would be the sum of its components.

  2. Cell polarization, which is an effect at the electrode/electrolyte interfaces. The causes are buildup of gas bubbles, concentration gradients that develop in the electrolyte, etc.

  3. Deterioration of the electrodes and/or electrolyte, particularly under high current drain.

  4. Of course, as @MaxW states, a major factor is cell geometry: area of electrodes and separation due to insulators and electrolyte.

For these reasons, though the maximum current can be calculated from the resistances and EMF, in actual use, cells often fall far short of their theoretical potential (no pun intended).

The resistance of a battery is primarily the sum of that of the cells. Since cells are joined with metallic connections, the cell-to-cell resistance is usually negligible (though I've used poorly designed battery holders with high-resistance spring contacts that severely limited the current, and that damaged the plastic holder due to ohmic heating).

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    $\begingroup$ I think you missed a large factor which is electrode's surface area. A wire or a plate doesn't matter for EMF, but it has a large effect on current. $\endgroup$ – MaxW Mar 22 '16 at 21:37
  • $\begingroup$ so if i have a salt electrolyte which is very dilute (i.e. 0.001M) will that be a poor conductor since their is not only less ions available but also because there is a lot of DI water (and DI water is a poor conductor)? $\endgroup$ – user510 Mar 22 '16 at 22:30
  • $\begingroup$ @MaxW is the electrode surface area the are that is in contact of the electrolyte or does it count the whole electrode (also the part that is not in contact with the electrolyte). Also, why will surface area have a large effect? Aren't most metal conductors (like aluminum and platinum) good conductors? $\endgroup$ – user510 Mar 22 '16 at 22:33
  • $\begingroup$ @user510 - Think... If you take the electrodes out of the solution how much current do you think will flow?!? $\endgroup$ – MaxW Mar 22 '16 at 22:41
  • $\begingroup$ yes, no doubt that surface area will contribute to conductance, but is it that significant? I am saying this because when I made a cell and dipped more of my electrode in the electrolyte solution, the current went up only a little. Also is the surface area of the electrode just the area that is in contact? Specifically, when I am calculating resistance of the electrode, is the surface area the same as cross section area? $\endgroup$ – user510 Mar 22 '16 at 22:52

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