<p>As in the ideal gas law, the universal gas constant allows for calculation of amount of energy associated with a certain group of molecules (see <a href="https://en.wikipedia.org/wiki/Gas_constant">https://en.wikipedia.org/wiki/Gas_constant</a>).  As the Nernst equation compares the "osmotic pressure" to "electrical pressure", the universal gas constant is needed to convert amount of an ion on the two sides of a membrane ("osmotic concentrations") to the amount of energy associated with that concentration differential ("osmotic pressure").  </p>

<p>Carefully looking at the units of all of the constituents of the equation can help clear things up.  R is in units of J / (mol * degree), and V is J/coulomb.  zF in the denominator gets you your coulombs.<br>
In short, both the left and right sides of the equation are more or less measures of energy.  R converts amounts of ions to the energy associated with their osmotic pressure so that it can be compared with the electrical energy associated with their charge.</p>

CC BY-SA 3.0
2016-07-11T21:19:58.750Z
Thank you so much! That adds some sense to my knowledge about R now !
Saran
CC BY-SA 3.0
2016-07-11T18:02:31.903Z
2016-07-11T18:09:49.580Z
2016-07-11T18:09:49.580Z
honi
<p><a href="https://en.wikipedia.org/wiki/Nernst_equation" rel="nofollow">The Nernst equation</a> is an equation that relates the the total voltage, i.e. the electromotive force, of the full cell at any point in time to the standard electrode potential, temperature, activity, and reaction quotient of the underlying reactions and species used. I have been wondering why <a href="https://en.wikipedia.org/wiki/Gas_constant" rel="nofollow">Universal gas constant (R)</a> is included in Nernst and Goldmann equations while describing the steady state of membrane potential?</p>

CC BY-SA 3.0
2016-07-11T08:45:21.827Z
I'm voting to close this question as off-topic because this should go to 
physics
AliceD
CC BY-SA 3.0
2016-07-11T14:29:00.640Z
Are questions about neuron membrane properties off-topic here?  I see a lot of them around, so I am not clear why this is any different.  If such questions are off-topic, then this would be on-topic for the proposed `Neuroscience` stack exchange site on Area 51.
TheBlackCat
CC BY-SA 3.0
2016-07-11T15:59:37.323Z
@TheBlackCat, if the question is relevant for understanding membrane potentials, we ask the OP (or anyone else) to add that part in the post. Not everybody is knowledgeable about neuroscience at such a detailed level. Providing more **context** to the question would prevent ambiguity and confusion of the topic.
Robin Kramer-ten Have
CC BY-SA 3.0
2016-07-11T16:23:05.823Z
@RobinKramer: It is at the end of the post, "...while describing the steady state of membrane potential?"
TheBlackCat
CC BY-SA 3.0
2016-07-11T16:31:50.567Z
You are absolutely right. I completely missed that part of the question. Then, since two people apparently missed it, perhaps some more emphasis on the neuro part may be handy, also to avoid further confusion :)
Robin Kramer-ten Have
CC BY-SA 3.0
2016-07-11T18:16:45.283Z
@RobinKramer - I noticed the Nernst / Goldmann equations mentioned and close-voted nonetheless; this is the realm of physics. I expect the quality of answers on that site to surpass the knowledge of anyone here. Nonetheless, I upvoted Honi's answer - it looks as fine an answer to the confines of this community.
AliceD
CC BY-SA 3.0
2016-07-11T21:26:34.623Z
Thank you @RobinKramer, TheBlackCat, Christiaan.I admit that my question lacked clear context. Thanks for your valuable edits :)
Saran
<neuroscience><theoretical-neuroscience><electrophysiology>
What is the role of (why )universal gas constant in Nernst equation?
Saran
# What is the role of (why )universal gas constant in Nernst equation?

(Asked by: username_0 on 2016-07-10)

[The Nernst equation](https://en.wikipedia.org/wiki/Nernst_equation) is an equation that relates the the total voltage, i.e. the electromotive force, of the full cell at any point in time to the standard electrode potential, temperature, activity, and reaction quotient of the underlying reactions and species used. I have been wondering why [Universal gas constant (R)](https://en.wikipedia.org/wiki/Gas_constant) is included in Nernst and Goldmann equations while describing the steady state of membrane potential?

**Tags:** neuroscience, theoretical-neuroscience, electrophysiology

> **Comments:**
> **username_1**: I'm voting to close this question as off-topic because this should go to  physics  
> **username_2**: Are questions about neuron membrane properties off-topic here?  I see a lot of them around, so I am not clear why this is any different.  If such questions are off-topic, then this would be on-topic for the proposed `Neuroscience` stack exchange site on Area 51.  
> **username_3**: @username_2, if the question is relevant for understanding membrane potentials, we ask the OP (or anyone else) to add that part in the post. Not everybody is knowledgeable about neuroscience at such a detailed level. Providing more **context** to the question would prevent ambiguity and confusion of the topic.  
> **username_2**: @RobinKramer: It is at the end of the post, "...while describing the steady state of membrane potential?"  
> **username_3**: You are absolutely right. I completely missed that part of the question. Then, since two people apparently missed it, perhaps some more emphasis on the neuro part may be handy, also to avoid further confusion :)  
> **username_1**: @RobinKramer - I noticed the Nernst / Goldmann equations mentioned and close-voted nonetheless; this is the realm of physics. I expect the quality of answers on that site to surpass the knowledge of anyone here. Nonetheless, I upvoted Honi's answer - it looks as fine an answer to the confines of this community.  
> **username_0**: Thank you @RobinKramer, username_2, Christiaan.I admit that my question lacked clear context. Thanks for your valuable edits :)  

---

## 1 answers

### Answer by username_4 on 2016-07-11. Score: 6 | Accepted answer

As in the ideal gas law, the universal gas constant allows for calculation of amount of energy associated with a certain group of molecules (see <https://en.wikipedia.org/wiki/Gas_constant>). As the Nernst equation compares the "osmotic pressure" to "electrical pressure", the universal gas constant is needed to convert amount of an ion on the two sides of a membrane ("osmotic concentrations") to the amount of energy associated with that concentration differential ("osmotic pressure").

Carefully looking at the units of all of the constituents of the equation can help clear things up. R is in units of J / (mol \* degree), and V is J/coulomb. zF in the denominator gets you your coulombs.  
In short, both the left and right sides of the equation are more or less measures of energy. R converts amounts of ions to the energy associated with their osmotic pressure so that it can be compared with the electrical energy associated with their charge.

> **Comments:**
> **username_0**: Thank you so much! That adds some sense to my knowledge about R now !  

---

