Activity Coefficients The Effect of Pressure and Temperature

The effect of pressure on the activity coefficient - at a constant temperature and composition - is given by  

Consider for example the case of water(l) in its mixture with methanol(2) at the conditions of Example 11.1 Xj = 0.7 T = 25 C P = 1 atm, where its partial molar excess volume is 0.3 cm /mol. Assuming this value to be independent of pressure for small pressure ranges, then the activity coefficient of water at some pressure P2, say 5 atm, relative to its value at 1 atm is given by  

We conclude, therefore, that - in the typical nonideal solution - the activity coefficient  

---