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Chapter: 11th 12th std standard Class Organic Inorganic Physical Chemistry Higher secondary school College Notes

Numerical values of gas constant (R)

Numerical values of gas constant (R)
The numerical value of the gas constant `R' depends upon the units in which pressure and volume are expressed, R = PV / T (assuming one mole of gas)

 

Numerical values of gas constant (R)

 

The numerical value of the gas constant `R' depends upon the units in which pressure and volume are expressed,

R  =            PV / T         (assuming one mole of gas)

R       = (Pressure x Volume) / Temperature

          = (     Force / Area )  x ( Volume / Temperature )

                            

Since Volume =    Area x length

         

R   = ( Force x Length ) /         Temperature

          = Work / Temperature

The dimensions of R are thus energy per degree per mole.

 

i) In litre - atmosphere

 

One mole of gas at S.T.P occupies a volume of 22.4 litre and thus

At STP

P = 1 atm R = PV/T (for 1 mole)

V =    22.4 litre R =        (1 x 22.4)/273

T = 273 K        R = 0.0821 litre atm K-1mol-1

= 0.0821 dm3.atm K-1mol-1

(ì 1 litre = 1 dm3)

 

ii) In C.G.S. System

 

At STP 1 mole of gas has

P = 1 atm = 1 x 76 x 13.6 x 980 dyne cm-2

= 1.013 x 106 dyne cm-2

V =  22400 cm3; T = 273 K

R = PV / T  = 1.013 x 106 x 22400  / 273

R  =  8.314 x 107 erg K-1 mol-1

 

iii) In M.K.S. System

 

In MKS or SI units, the unit of R is joule

Since 107 erg        =       1 Joule

R = 8.314 Joule K-1 mol-1

1 calorie = 4.184 Joule

R = 1.987 cals deg-1 mol-1

 

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11th 12th std standard Class Organic Inorganic Physical Chemistry Higher secondary school College Notes : Numerical values of gas constant (R) |


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