(a) What is the basis for the group contribution methods in the prediction of activity coefficients? What are UNIQUAC and UNIFAC methods?

(b) Under atmospheric condition the acetone-chloroform azeotrope boils at \(64.6^{\circ} \mathrm{C}\) and contains \(33.5 \mathrm{~mol}\) percent acetone. The vapour pressures of acetone and chloroform at this temperature are 995 and \(855 \mathrm{~mm} \mathrm{Hg}\) respectively. Calculate the composition of the vapour at this temperature in equilibrium with a liquid analyzing 11.1 mole percent acetone, given the van Laar equation \[ \ln \gamma_{1}=\frac{A x_{2}^{2}}{\left(\frac{A}{B} x_{1}+x_{2}\right)^{2}} \quad \text { and } \quad \ln \gamma_{2}=\frac{B x_{1}^{2}}{\left(x_{1}+\frac{B}{A} x_{2}\right)^{2}} \]