Why aren't electrolytic cells usually separated?

Galvanic cells need to be separated so that electrons will be forced to move through the external circuit, but I was wondering why electrolytic cells are usually not kept separated but rather as a single cell? Is it just convenience or do the reactions take place differently if the two electrodes of an electrolytic cell were to be separated?





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> Galvanic cells need to be separated so that electrons will be forced to move through the external circuit [...]
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In a Galvanic cell, the reaction has a negative Gibbs energy of reaction. If the reactants are allowed to come in contact, the reaction proceeds without generating electricity (generating more heat instead). In some cases (like a lead acid battery), the reactants can't come into contact because they are both in the solid state, one on the anode and the other on the cathode. In other cases, they would come into contact, so there has to be a barrier (and separate half-cells).



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> [...] but I was wondering why electrolytic cells are usually not kept separated but rather as a single cell?
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In an electrolytic cell, the reaction has a positive Gibbs energy. If the products are allowed to come into contact, they would react (unless there is a need for a catalyst) in the reverse direction, leading to a futile cycle. In many cases (where the products are gases or solids or liquids that don't mix with the electrolyte), the products are unable to come into contact, like in molten NaCl electrolysis. In other cases, like the electrolysis of water, the products could potentially mix in the gas phase but are not sufficiently reactive to support the reverse reaction (for water electrolysis, you would have to collect oxygen and hydrogen in a common vessel and then ignite them with a spark, either on purpose or by accident).



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> Is it just convenience or do the reactions take place differently if the two electrodes of an electrolytic cell were to be separated?
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You can't make a generalization. It depends on the specific reaction.


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@planckton. Galvanic cells need not to be "separated" as you state. What has to be separated is not the cells, but the half-cells. In the Daniell cell, Zinc is the anode and emits electrons which move through the external circuit. But this phenomena also produces $\ce{Zn^{2+}}$ ions in solution. This is only possible if some negative ions are present in solution. These negative ions are coming from the cathode region, which is filled with $\ce{CuSO4}$ solution. As the $\ce{Cu^{2+}}$ ions are discharged by the incoming electrons, the sulfate ions are repelled, and must leave : they cross the membrane or the bridge between the two half-cells, to arrive in the anodic solution, where the $\ce{Zn^{2+}}$ ions are attracting them.


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