Consider a pure liquid A in a capillary of diameter D as shown in the figure. As evaporation proceeds, liquid A is slowly added from the bottom of the capillary tube to keep the liquid-gas interface constant. We are interested in the molar rate of evaporation of species A from the liquid surface into a gaseous mixture of A and B. The problem will be analyzed under the following assumptions: Consider the steady state Species A and B form an ideal gas mixture. Species B have negligible solubility in liquid A The entire system is held at constant temperature and pressure The diffusion coefficient is constant There is no chemical reaction between species A and B