## Gas constant, R

Volume: $\Delta S = nR\ln \frac{V_{2}}{V_{1}}$
Temperature: $\Delta S = nC\ln \frac{T_{2}}{T_{1}}$

Aschreck 2G
Posts: 9
Joined: Fri Sep 25, 2015 3:00 am

### Gas constant, R

How do you determine which value of R to use in calculations, 8.314 or .0821??

Malaya Du 2G
Posts: 8
Joined: Fri Sep 25, 2015 3:00 am

### Re: Gas constant, R

It depends on what units are needed for the problem. .082 is in L atm/ K mol while 8.314 is in J/K mol. Usually we use 8.314 because we are dealing with Joules.

Daniel Fu 2K
Posts: 10
Joined: Fri Sep 25, 2015 3:00 am

### Re: Gas constant, R

8.31 J K^−1 mol^−1 is used when you have the gas quantity in moles, pressure in N/m^2, T in ºK and volume in m^3

0.0821 L atm K^−1 mol^−1is used when you have the gas quantity in moles, the volume in L, pressure in atm and T in ºK

But in case you forget, just make sure you know the units associated with the numbers and just try and use the one that makes the unit cancellation work out.