Surface Tension of Regular Solutions Defay et al

Example 1.7 Surface Tension of Regular Solutions (Defay et al., 1966) 

Assume that dimethyl ether (1) and acetone (2) form regular solutions at 15°C, where Yi = 17.6 and Y2 = 23.7 mN/m. The interchange energy parameter a may be taken as 1.88 k /g-mol and the area per molecule as 0.30 nm . Calculate the surface tension and surface composition of a hquid mixture having = 0.7. Make two calculations, one for a simple cubic lattice ( = 2/3, m = 1/6) and one for a close packed lattice ( = 1/2, m = 1/4). Compare your results with the predictions of ideal solution theory and with the experimental value of 20.7 mN/m. 

From Equations 1.72 and 1.74 for an ideal solution the corresponding values are 

Qearly the calculations based on regular solution theory are in better agreement with the experimental measurement. 

---