Numerical Value of R and Units

(1).     At N. T. P

P   =  1atm,        T = 273K.

V  =   22.4 lit,   n = 1 mole.

R   =(P ×V)/ (n × T)   =  (1 atm. × 22.4 lit) / (1 mol  × 273K) =   0.821 atm lit deg^-1 mol^-1

Now a day’s at N. T. P        

P = 1bar   (At P = 1bar, Volume occupied by 1 mole is 22.7 lit instead of 22.4 lit at 1 atm.)

V = 22.7 lit,  

n = 1 mol.

T = 273K

R = (1 bar × 22.7 lit) / (1 mol × 273K) 

    =       0.083 bar lit mol^–1 degree^–1  

(2).     In C. G. S Units

P  = 76cm of Hg,  r of Hg  = 13.6 gm/ml            

P    =   ρhg

=   76 × 13.6 × 9.81 dynes/cm²

V     =   22400 ml

T     =   273 K

n     =    1mol

R   =   (76 × 13.6 ×9.81) × 22400 dynes/cm²× ml. × degree^–1 mol^–1

R   =    8.314 × 10⁷ ergs degree^–1 mol^–1

(3).     In S. I Units

1 J  =   10⁷ ergs.

R   =   8.314 J degree^–1 mol^–1

(4).     In terms of Calories

1 Cal.   =   4.18 J.

R    =  8.314/4.18  cal. degree^–1 mol^–1

      =   1.987 calories degree^–1 mol^–1