In: Chemistry
A mixture of benzene and toluene is in equilibrium with its vapor at 50oC. What mole fraction of benzene is in the vapor phase? You may assume that this system follows Raoult's Law. Note: when solving Antoine's equation it is best to keep all sig figs through calculation and then truncate them at the end.
Apply Raoults Equations in equilibrium
x1*P°1 = y1*PT
x2*P°2 = y2*PT
T = temperature in °C
P°1 = vapor pressure for benzene; from antoine equations (bar)
log10(P) = A − (B / (T + C)) A,B,C = 4.72583 1660.652 -1.46
P°2 = vapor pressure for toluene ; from antoine equations
log10(P) = A − (B / (T + C)) A,B,C = 4.23679 1426.448 -45.957
also
x2 = 1-x1 and y2 = 1-y1; Pt total pressure
substitute
x1*10 ^(4.72583 - 1660.652/ (T-1.46) ) = y1*PT
(1-x1)*10 ^(4.23679 - 1426.448 / (T-45.957) ) = (1-y1)*PT
T = 50°C
x1*10 ^(4.72583 - 1660.652/ (273+50-1.46) ) = y1*PT
(1-x1)*10 ^(4.23679 - 1426.448 / (273+50-45.957) ) = (1-y1)*PT
simplify
0.36403x1 = y1*PT
0.12244(1-x1) = (1-y1)*PT
Assume Pressure is 1 atm, so P = 1 bar approx
0.36403x1 = y1*1
0.12244(1-x1) = (1-y1)*1
simplify
y1 = 0.36403*x1
0.12244-0.12244*x1 = 1-y1
0.12244-0.12244*x1 = 0.36403*x1
(0.36403 + 0.12244)*x1 =0.12244
x1 = 0.12244 / ((0.36403 + 0.12244)) = 0.2516
so
y1 = 0.36403*x1 = 0.36403*0.2516 = 0.09158