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Depending on which value you use, R can have the constants: J*K-1*mol-1, L*atm*K-1*mol-1, L*bar*K-1*mol-1, or L*Torr*K-1*mol-1. You use the various values of R based on the other variables used, make sure all the units cancel out and you are left with the units you are trying to find.
The units for R vary depending on which of the Rs you want to use. Usually you will be using 8.314 J/molK or 0.08206 Latm/molK. Make sure to look at what the problem gives you and what the problem wants in regards to units.
These units vary. Always write out your units for calculations, just so you know what R value is needed to solve. In order to get the write answer you need to use the correct R based off of what's asked for and what units are given.
There are various ways in which one can use the constant R and so there are various units for the constant. For example, in the PV=nRT equation, one side has atm*L and the other as mol*K*R, and so to cancel so they equal each other, R has the unit and value of 0.08206 atm*L/mol*K. However, for work, w= nrTln[(v2-v1)] and so we need the final result to have joules as the unit so R has the value and unit of 8.314 joules/mol*K .
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