Question

Nitrogen gas is compressed isothermally at 250K from 1.0 bar to 150 bars. Determine the change in enthalpy and entropy using:
a. Redlich-Kwong equation of state
b. Using tabular superheat data

Answer 1

The Redlich–Kwong equation is formulated as:

where:

• P is the gas pressure
• R is the gas constant,
• T is temperature,
• V_m is the molar volume (V/n),
• a is a constant that corrects for attractive potential of molecules, and
• b is a constant that corrects for volume.

The constants are different depending on which gas is being analyzed. The constants can be calculated from the critical point data of the gas:^[1]

where:

• T_c is the temperature at the critical point, and
• P_c is the pressure at the critical point.

entha;py change = - nRT2.303 log (PA/PB) =    1 * 8.314 * 250 *2.303 log (1/150)    = -10416.48L       

        = -1.041648KJ

     entropy change   = nR *2.303 *log PA/PB   = 1* 8.314 *2.303 log (1/150)    = -41.666 J/K