The R in the equation PV=nRT which is the most common form of Boyle's Ideal Gas Law.

R has a value of 0.08206 (L)(atm)/(mol)(K)

If your units of pressure (P) happen to be in kilopascals (kPa), then the value of R, the Universal Gas Constant, is: 8.314 (kPa)(L)/(K)(mol)

In many thermodynamics calculations, it is often easier to choose the Universal Gas Constant in appropriate units, instead of converting the units of each physical property. Following is a list of most commonly used values of the Gas Constant:
8.31451      Jmol-1K-1
8.31451 kJ • kmol-1 • K-1
8.31451 m3Pa • mol-1 • K-1
8.31451•10-3 kJ • mol-1 • K-1
8.31451•10-2 Lbar • mol-1 • K-1
8.31451•101 cm3 • bar • mol-1 • K-1
8.31451•103 cm3 • kPa • mol-1 • K-1
8.20578•101 cm3atm • mol-1 • K-1
8.20578•10-2 L • atm • mol-1 • K-1
6.23640•104 cm3torr • mol-1 • K-1
6.23640•101 L • torr • mol-1 • K-1
1.98589 cal • mol-1 • K-1
1.98589 Btulbmol-1R-1
7.30245•10-1 ft3 • atm • lbmol-1 • R-1
1.07316•101 ft3psi • lbmol-1 • R-1
1.54536•103 ft• lbf • lbmol-1 • R-1
The universal gas constant is also extremely useful in chemical thermodynamics, as in the equation:

delta G = delta G (STP) + R * T * ln(Q)

delta G: the change in free energy of a reaction
delta G (STP): the known change in free energy at standard temperature and pressure (25 degree celsius, 1 atm).
R: universal gas constant
T: absolute temperature
Q: reaction quotient

Since G is in joules/mole, T is in Kelvin, and Q is in ignored log units, the first expression of R (8.31451 J/mol*k) is used when the other quantities are in SI units.

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