Universal Gas Constant

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      J • mol-1 • K-1

8.31451      kJ • kmol-1 • K-1

8.31451      m3 • Pa • mol-1 • K-1

8.31451•10-3 kJ • mol-1 • K-1

8.31451•10-2 L • bar • 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  cm3 • atm • mol-1 • K-1

8.20578•10-2 L • atm • mol-1 • K-1

6.23640•104  cm3 • torr • mol-1 • K-1

6.23640•101  L • torr • mol-1 • K-1

1.98589      cal • mol-1 • K-1

1.98589      Btu • lbmol-1 • R-1

7.30245•10-1 ft3 • atm • lbmol-1 • R-1

1.07316•101  ft3 • psi • 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.