Maintaining Charge Separation: The Role of EMF in Electrochemical Cells

[tonyjk]

Hello,
I have a question concerning electrochemical cells or batteries. It is said that when the battery is at open circuit, it has small charge separation on its electrodes thus having a potential difference equal to the emf of the battery. When the battery is connected to a circuit, the emf of the battery maintain this charge separation so the same potential difference. My question is the emf of the battery, due to oxydation-reduction reaction, how does it maintain or how does it provides a "force" to maintain the charge separation. Here an analog study : http://www.wired.com/2015/02/battery-doesnt-store-charge-work/ where the belt is used as an analogy of the chemical reaction "force".

Thank you

 

[Simon Bridge]

The cell produces ions in a chemical reaction and the material of the cathode and anode favorably attracts a particular charge. You can get more details online... different batteries have different chemistries.

 

[tonyjk]

The cell produces ions in a chemical reaction and the material of the cathode and anode favorably attracts a particular charge. You can get more details online... different batteries have different chemistries.

so a chemical reaction produces ions thus maintaining the charge separation. But why the battery cannot maintain for infinite time thus discharging?

 

[Simon Bridge]

Details depend... but eventually you run out of reactants.

 

[tonyjk]

I was reading about galvanic cell. On the anode side the zinc is losing electrons and on the cathode side the cupper is gaining electron. We put salt bridge, to maintain the neutrality of the solution i.e SO4 2- will move to anode side and Na+ to the cathode side. Does an electric field cause their movement? or it is a diffusion current of the ions? When there's no wire connecting anodes and cathodes, is there electrons on the anode side? Thus having charge separation and voltage?

 

[Simon Bridge]

If you look at the charges of the moving ions and the charges of the anode and cathode... see?
Though, all chemistry is down to electric fields... you can see how complicated chemistry gets.

Note: Cu is cuprum, commonly known as copper... a "cupper" is a strong brownian motion producer commonly used to help generate finite amounts of improbability.