Answer to Question #163566 in Chemical Engineering for Joseph

Question

diffusivity of gas pair oxygen carbon tetrachloride is determined by observing steady state evaporation of carbon tetrachloride.The distance between carbon tetrachloride liquid level and the top of the tube is 17.1cm.the total pressure of the system 755mmHg.The vapour pressure of carbon tetrachloride at this temperature is 33mmHg.The cross sectional area of the two is 0.82cm^2.If it is found that 0.0208cm^3 of CCL4 evaporate in 10hours period.What is the diffusivity of gas pair carbon tetrachloride

Answer 1

Diffusion coefficient is the proportionality factor D in Fick's law (see Diffusion) by which the mass of a substance dM diffusing in time dt through the surface dF normal to the diffusion direction is proportional to the concentration gradient grad c of this substance: dM = −D grad c dF dt.

Direct methods evaluate the diffusion coefficient by measuring concentration of the diffusing species (solvent) as a function of depth of penetration. ... The diffusivity is estimated by using compositional analysis techniques. Mass diffusivity increases with temperature and decreases with pressure.