Why is the electrolytic cell non spontaneous?

[funsmith]

If oxidation happens at the anode, both in the galvanic cell and electrolytic cell, then why won't electrons just flow out to the cathode and (DELTA)G Negative?

Thanks.

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[loveoforganic]

Electrolytic cells are, by definition, nonspontaneous, just like galvanic (voltaic) cells are, by definition, spontaneous. In an electrolytic cell, the electrons will be pushed in the direction opposite that of the same galvanic cell.

 

[Cjc555777]

The reason it is non-spontaneous is because electrolytic cells are just two compounds that without an electrical current don't want to reaction (have a positive delta G). You can force them to react by sending an electrical current through a circuit. The non-spontaneous thing has NOTHING to do with what is going on while you are sending the electrical current through the system. It is just referring to what the the mixture would do it it was just sitting in a beaker, which is nothing.

 

[loveoforganic]

That's not true. They could very well react vigorously - the electricity is just applied to get them to react in the direction opposite how they'd react in a galvanic cell.

 

[Cjc555777]

That's not true, because if you combine the two cells of a galvonic cell with the intention of putting electrical current through it to go in the reverse direction, those two species will react with each other ONLY in the forward direction.

 

[linkin06]

because G = -nFEcell

so in electrolytic cells, Ecell is a negative number, and hence G = a positive number, meaning nonspontaneous

 

[Cjc555777]

Exactly, a negative E means the reaction won't proceed, which means the reactants won't react without help!

 

[loveoforganic]

***They won't react in the direction you want them to***

The cell Ag+|Ag||Li+|Li has a very, very negative E, as written. However, if you were to make that cell, a reaction WOULD occur, most definitely. Regardless of the conventions about the order they're written implying anode/cathode respectively, if you were to make that cell, electrons would flow, and Ag+ would be reduced. To make that cell electrolytic, and to run as written, you would have to apply current to the Ag+/Ag electrode.

 

[funsmith]

Thanks folks. I seem to get a grip on it now.