Q6. A diffusion cell is used to measure binary molecular diffusivities. It consists of a chamber closed at one end by a fine porous glass disc. Porous Disc my In use, the chamber is filled through the stopcock with a pure gas, the stopcock is closed, and the cell is immersed in the other gas. Analysis of the gas in the cell is obtained continuously by an internal thermal conductivity device. The cell has been calibrated with hydrogen-air at 0C and 1 atm. DAB = 2.37 ft?/hr by noting the time it took for the internal concentration to fall to 20 % of its original value was 1 hour and 17 minutes. The molecular diffusivity of phosgene is measured similarly at 20C and 1 atm. It is found that the concentration reaches half of its original concentration in 8 hours and 51 minutes. What is the molecular diffusivity of phosgene at 20C? Assumption: steady state conditions. (15 points)