Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: scientizscht on 03/05/2020 11:48:36

Title: Are voltaic cells in equilibrium?
Post by: scientizscht on 03/05/2020 11:48:36

Hello

So when you have a voltaic cell, you have two redox half reactions that make the two solutions positively and negatively charged.

This induces the movement of ions through the salt bridge.

My question is, during the time when the cell is functioning and producing electricity, is the movement of ions through the salt bridge exactly equal to the movement of the electrons and the movement of the Zn, Cu ions into and out of the electrodes?

Or for the cell to work, the flow of electrons needs to be always slightly higher than the move of the ions in the salt bridge?

Also, is the ion movement via the salt bridge instant or it delays and allows some charge to be built up in the solutions?

Thanks

Title: Re: Are voltaic cells in equilibrium?
Post by: evan_au on 03/05/2020 23:45:38

An equilibrium is where there is no overall change in the composition of the system (even though individual atoms may be changing state, there will be an equal number changing in the opposite direction).

If we take the classic copper/zinc voltaic cell: for the entire time that a voltaic cell is delivering current, one electrode will be dissolving. This is not an equilibrium
- The current will only stop when the electrode is completely dissolved. Then it is in an equilibrium.

Similarly, when there is no current flowing, the cell is (almost) in equilibrium.