A gas of unknown initial concentration is separated from a mixture with air as it passes through a 5.0 cm thick plate of

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A gas of unknown initial concentration is separated from amixture with air as it passes through a 5.0 cm thick plate ofpolymer. Knowing that the diffusivity of the gas in the plate is3.5 x 10-5 m²/s and its concentration at the surface ofthe plate before diffusion is 0.50 kg/m³ and that after 5 secondsof diffusion it reaches a concentration of 0.45 kg/m³ in half ofthe plate, what is its concentration at the beginning of theprocess? The process is non-stationary.