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usivity @0°C, 1 atm. D = 0.144 cm²/s] 14 Question 3 The departure from equilibrium conditions is the impetus for species mass transfer across a phase boundary. A) Distinguish between steady-state mass transfer condition and equilibrium condition (4 marks] B) At equilibrium the concentration of the diffusing species is the same in all phases. (Yes or No) Why? [3 marks] C) Helium gas at 25°C and 4 bars is stored in a spherical fused silica (SiO2) container of 200 mm internal diameter and 10 mm thickness. The pressure of helium on the outside of the container is negligible. i) ii) Determine the steady-state equation for radial direction helium concentration profile [C = f(r)] across the container wall Calculate the steady-state (radial direction) rate of helium mass loss from the [9 marks] container [Data: Atomic weight, He = 2; He-SiO₂ diffusivity @ 20°C, D = 0.4 x 10-13 m²/s; Solubility of He [9 marks] in SiO2, S = 0.45 x 10-3 kmol/m³ bar]