What is a Liquid/Liquid Junction Potential and Its Role in Batteries?

[somasimple]

TL;DR

Liquid junction potential question

Hi,
Is there a liquid/liquid junction potential between two liquids of same composition but different concentrations WHEN there is no external electrical circuit and then NO electrodes? (Of course this potential is not measurable).

Thanks,

 

[atyy]

Yes, because the solutions are themselves conductors. Usually, we would say that the potential is measurable.

https://mdc.custhelp.com/app/answer...opatch:-measure-the-liquid-junction-potential
http://junctionpotential.blogspot.com/2010/10/how-do-i-measure-liquid-junction.html

 

[somasimple]

Well, the links you gave show electrodes then there is a RedOx reaction with charge transfer within the external circuit. That is not my question.

 

[Tom.G]

Summary:: Liquid junction potential question

Of course this potential is not measurable

If something is not detectable, then how would anyone know?

 

[somasimple]

The theory says it may exist but it not directly measurable. => from this book
https://link.springer.com/book/10.1007/978-1-4613-4560-2

 

[atyy]

Yes, from the mechanism it exists even without being measured.

 

[somasimple]

Thanks for this reply.

 

[atyy]

There is a somewhat similar phenomenon at metal-metal conductor junctions. This phenomenon is not strictly needed in a thermocouple, but it is often used.
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/tcoup.html
https://www.explainthatstuff.com/howthermocoupleswork.html
https://nptel.ac.in/content/storage2/courses/113106065/Week 4/Lesson9.pdf

 

[somasimple]

Thanks again Atyy,
The same phenomenon applies to batteries. They have an internal EMF even if they are not connected but one can not know their inner potential without connecting them. The charge separation creates an Electric field also called an electroneutrality field. It is the force that let's the things in place.