The Soave-Redlich-Kwong equation iswhere b = 0.08664RTc/Pc (as in the Redlich-Kwong equati...

The Soave-Redlich-Kwong equation is

where b = 0.08664RTc/Pc (as in the Redlich-Kwong equation) and a(T) is the following function of temperature:

a(T)= 0.42748(R2Tc2/Pc){1 + m[ 1 − (T/Tc)0.5]}2

m = 0.480ω + 1.574 - 0.176ω2

The quantity ω is the acentric factor of the gas, defined as

where Pvp is the vapor pressure of the liquid at T= 0.7Tc. The acentric factor is close to zero for gases with approximately spherical molecules of low polarity. A tabulation of ω values is given in Appendix A of Poling, Prausnitz, and O’Connell. The Soave-Redlich-Kwong equation has two parameters a and b, but evaluation of these parameters requires knowing three properties of the gas: Tc, Pc, and ω. For propane ω = 0.153. (a) Show that a(T) = 1.082 × 107 atm cm6 mol−2 for propane at 25°C. (b) Use the Soave-Redlich-Kwong equation to find the vapor pressure and saturated liquid and vapor molar volumes of propane at 25°C. The Redlich-Kwong spreadsheet of Fig. 8.6 can be used if the T1/2 factors in the denominators of all for­mulas are deleted.