At 60° C, vapour pressure of methanol and water are 84.562 kPa and 19.953 kPa respectively. An aqueous solution of methanol at 60° C exerts a pressure of 39.223 kPa; the liquid phase and vapour phase mole fractions of methanol are 0.1686 and 0.5714 respectively. Activity co-efficient of methanol is__________________?

Question

Accepted Answer

1.572. Using Raoult's Law, partial pressure of methanol is y*x_total = 0.5714 * 39.223 = 22.416 kPa. Activity coefficient gamma = P_partial / (x_liquid * P_vapor) = 22.416 / (0.1686 * 84.562) ≈ 1.572.