Sub-limitation of small iodine spheres in still air. A sphere of iodine, 1 cm in diameter, is placed in still air at 40°C and 747 mm Hg pressure. At this temperature the vapor pressure of iodine is about 1.03 mm Hg. We want to determine the diffusivity of the iodine-air system by measuring the sublimation rate. To help determine reasonable experimental conditions, 

(a) Estimate the diffusivity for the iodine-air system at the temperature and pressure given above, using the intermolecular force parameters in Table E.1. 

(b) Estimate the rate of sublimation, basing your calculations on Eq. 18.2-27. This method has been used for measuring the diffusivity, but it is open to question because of the possible importance of free convection.