Example 10.1: Ammonia gas is diffusing at a constant rate through a layer of stagnant air 1mm thick. Conditions are such that the gas contains 50 percent by volume ammonia at one boundary of the stagnant layer. The ammonia diffising to the other boundary is quickly absorbed and the concentration is negligible at that plane. The temperature is 295K and the pressure atmospheric, and under these conditions the diffusivity of ammonia in air is 0.18 cm2/s. Estimate the rate of diffusion of ammonia through the layer