galvanic cell vs electrolysis [closed]








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At school(high school), to calculate the voltage needed for electrolysis, we calculate the voltage produce if the elements were in a galvanic cell, preceded by a minus.
So if a galvanic cell with Cu and Cr would produce 1,14V, we would say that an electrolysis with Cu and Cr will need -1.14V. 


But why do we do this and is this correct?


Thank you in advance.




Suppose you have two galvanic cells A and B producing 1.14 V. If you connect them together, with both positive poles together, and both negative poles together, nothing will happen. No current will be produced. Now suppose that one of these two cells, say A, produces the same voltage 1.14 V, and B produces a little less than A, say 1.10 V. A works in a galvanic cell mode and will produce some current going through the second cell B. And this second cell B will work in the electrolysis mode, and the current through the cell B will go in the opposite direction with respect to its behavior in the galvanic cell mode. It looks as if B is going to be recharged. 


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