### Which gas constant, R, to use?

Posted:

**Tue Aug 23, 2011 5:42 pm**Can you clarify when R is 8.3145 and when R is .08206 ?

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=129&t=301

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Posted: **Tue Aug 23, 2011 5:42 pm**

Can you clarify when R is 8.3145 and when R is .08206 ?

Posted: **Tue Aug 23, 2011 5:42 pm**

In SI units, the real gas constant, R, is equal to 8.3145 Joules/mol K. However, if we express R in units of L atm/mol K, it's value is 0.08206. It's just a case of unit conversion. If we are calculating using the ideal gas equation PV=nRT then we use the .08206 because we will we will be calculating either L, atm, mol or K. If we are doing any kind of energy then we use 8.314 because we will need the J.

Posted: **Sun Oct 25, 2020 2:57 pm**

Chem_Mod wrote:In SI units, the real gas constant, R, is equal to 8.3145 Joules/mol K. However, if we express R in units of L atm/mol K, it's value is 0.08206. It's just a case of unit conversion. If we are calculating using the ideal gas equation PV=nRT then we use the .08206 because we will we will be calculating either L, atm, mol or K. If we are doing any kind of energy then we use 8.314 because we will need the J.

Wouldnâ€™t we also use the .08206 value for r in the density equation d=pm/rt ?