Consider steady-state evaporation of a spherical toluene (A), which is evaporating into a very large volume of still air (B). You may assume that the size of the sphere is relatively large and thus remains constant over the timescale of interest.

a. Starting with a shell balance, show that for a concentrated solute, the expression for yA as a function of r is given by:

YA= 1- (1- YA, sat)^Ro/r

(where Ro = radius of sphere, yAsat = equilibrium saturation mole fraction of toluene in air)

b. Using this expression for YA, show that you can recover the expression we derived for a dilute solution