You can convert between joules and L atm in the following manner:
First start with these basic unit conversions:
1 atm = 101.3 kPa
1 kPa = 1,000 N m
-2 = 1,000 kg m
-1 s
-21 L = 1 dm
3 = 0.001 m
31 J = 1 N m = 1 kg m
2 s
-2Therefore 1 L atm = 0.001 m
3 * 101.3 kPa = 0.1013 kPa m
3 = 101.3 N m
-2 * m
3 = 101.3 N m = 101.3 J.
With the conversion, 101.3 J = 1 L* atm, you should see that the two values of R are equivalent. Also, if you find the value of R when expressed in units of L kPa mol
-1 K
-1, you should find why 8.314 works when your pressure is in units of kPa.
Being comfortable interchanging between different sets of units is essential to doing any sort of science (remember, the
Mars Climate Orbiter crashed on Mars instead of orbiting it because the scientists in charge didn't use the proper units in their calculations). It is definitely worth reading over again/asking your teacher about.
[edit: correcting spelling mistake]